这个方法能解决：SetEnclosedBorderOfRegion()
1 //merged cells on mutiple rows 2 CellRangeAddress region = new CellRangeAddress(2, 4, 0, 0); 3 sheet.AddMergedRegion(region); 4 5 //set enclosed border for the merged region 6 ((HSSFSheet)sheet).SetEnclosedBorderOfRegion(region, BorderStyle.DOTTED, NPOI.HSSF.Util.HSSFColor.RED.index);
注意：如果新建行，边框会初始化。
参考：https://q.cnblogs.com/q/42580/
原文：http://www.cnblogs.com/loge/p/7181307.html