第一行默认是标题，可设置行【RowType】进行设置类型

            Document doc = Application.DocumentManager.MdiActiveDocument;

            using (Transaction tr = doc.TransactionManager.StartOpenCloseTransaction())
            {
                BlockTable bt = tr.GetObject(doc.Database.BlockTableId, OpenMode.ForRead) as BlockTable;
                BlockTableRecord btr = tr.GetObject(bt[BlockTableRecord.ModelSpace], OpenMode.ForWrite) as BlockTableRecord;

                Table table = new Table();
                //设置表格大小（必须先创建表格类型再设置表格属性）
                table.SetSize(5, 3);
                //设置行高
                table.SetRowHeight(50);
                table.SetColumnWidth(200);
                // 设置表格的行数和列数
                
                // 设置表格的位置和大小
                table.Position = new Autodesk.AutoCAD.Geometry.Point3d(0, 0, 0);

                //从（2，0）单元格合并至（2，1）单元格，行列下表从0开始
                var cellRange = CellRange.Create(table, 2, 0, 2, 1);
                table.MergeCells(cellRange);

                btr.AppendEntity(table);
                tr.AddNewlyCreatedDBObject(table,true);

                tr.Commit();
            }