The interface is prepared for NPOI 2.0 actually. In NPOI 2.0, there are two namespace: XSSF and HSSF. XSSF is for xlsx, HSSF is for xls. Both implements interfaces in NPOI.SS；
NPOI有3种dll：①XSSF操作xlsx格式版本的Excel；②HSSF操作xls格式版本的Excel；③SS以上两种格式的Excel都可操作；
下面的方式是使用SS的类下方法写的；

/// Description:  Inserts a existing row into a new row, will automatically push down
///               any existing rows.  Copy is done cell by cell and supports, and the
///               command tries to copy all properties available (style, merged cells, values, etc...)
/// 
private void CopyRow(IWorkbook workbook, ISheet worksheet, int sourceRowNum, int destinationRowNum)
        {
            // Get the source / new row
            IRow newRow = worksheet.GetRow(destinationRowNum);
            IRow sourceRow = worksheet.GetRow(sourceRowNum);

            // If the row exist in destination, push down all rows by 1 else create a new row
            if (newRow != null)
            {
                worksheet.ShiftRows(destinationRowNum, worksheet.LastRowNum, 1);
            }
            else
            {
                newRow = worksheet.CreateRow(destinationRowNum);
            }

            // Loop through source columns to add to new row
            for (int i = 0; i < sourceRow.LastCellNum; i++)
            {
                // Grab a copy of the old/new cell
                ICell oldCell = sourceRow.GetCell(i);
                ICell newCell = newRow.CreateCell(i);

                // If the old cell is null jump to next cell
                if (oldCell == null)
                {
                    newCell = null;
                    continue;
                }

                // Copy style from old cell and apply to new cell
                ICellStyle newCellStyle = workbook.CreateCellStyle();
                newCellStyle.CloneStyleFrom(oldCell.CellStyle); ;
                newCell.CellStyle = newCellStyle;

                // If there is a cell comment, copy
                if (newCell.CellComment != null) newCell.CellComment = oldCell.CellComment;

                // If there is a cell hyperlink, copy
                if (oldCell.Hyperlink != null) newCell.Hyperlink = oldCell.Hyperlink;

                // Set the cell data type
                newCell.SetCellType(oldCell.CellType);

                // Set the cell data value
                switch (oldCell.CellType)
                {
                    case CellType.Blank:
                        newCell.SetCellValue(oldCell.StringCellValue);
                        break;
                    case CellType.Boolean:
                        newCell.SetCellValue(oldCell.BooleanCellValue);
                        break;
                    case CellType.Error:
                        newCell.SetCellErrorValue(oldCell.ErrorCellValue);
                        break;
                    case CellType.Formula:
                        newCell.SetCellFormula(oldCell.CellFormula);
                        break;
                    case CellType.Numeric:
                        newCell.SetCellValue(oldCell.NumericCellValue);
                        break;
                    case CellType.String:
                        newCell.SetCellValue(oldCell.RichStringCellValue);
                        break;
                    case CellType.Unknown:
                        newCell.SetCellValue(oldCell.StringCellValue);
                        break;
                }
            }

            // If there are are any merged regions in the source row, copy to new row
            for (int i = 0; i < worksheet.NumMergedRegions; i++)
            {
                CellRangeAddress cellRangeAddress = worksheet.GetMergedRegion(i);
                if (cellRangeAddress.FirstRow == sourceRow.RowNum)
                {
                    CellRangeAddress newCellRangeAddress = new CellRangeAddress(newRow.RowNum,
                                                                                (newRow.RowNum +
                                                                                 (cellRangeAddress.FirstRow -
                                                                                  cellRangeAddress.LastRow)),
                                                                                cellRangeAddress.FirstColumn,
                                                                                cellRangeAddress.LastColumn);
                    worksheet.AddMergedRegion(newCellRangeAddress);
                }
            }

        }