首先，我們應該先新增一個引用在UI裡。

 這個方法有可能被多次用到，所以把它封裝在一個類裡邊，方便呼叫。

using System.Windows.Forms;//新增引用窗體
using Excel = Microsoft.Office.Interop.Excel;
using System.Data.OleDb;

namespace UI
{
    public class ToExcel
    {
        public void RExcel(DataGridView dgv)
        {
            if (dgv.Rows.Count == 0)
            {
                MessageBox.Show("沒有資料");
                return;
            }
            
            string fileName = "";
            string saveFileName = "";
            SaveFileDialog saveDialog = new SaveFileDialog();
            saveDialog.DefaultExt = "xlsx";
            saveDialog.Filter = "Excel檔案|*.xlsx";
            saveDialog.FileName = fileName;
            saveDialog.ShowDialog();
            saveFileName = saveDialog.FileName;
            if (saveFileName.IndexOf(":") < 0) return;//被點了取消
            Microsoft.Office.Interop.Excel.Application xlApp = new Microsoft.Office.Interop.Excel.Application();
            if (xlApp == null)
            {
                MessageBox.Show("無法建立Excel物件，您的電腦可能未安裝Excel");
                return;
            }
            Microsoft.Office.Interop.Excel.Workbooks workbooks=xlApp.Workbooks;
            Microsoft.Office.Interop.Excel.Workbook workbook = workbooks.Add(Microsoft.Office.Interop.Excel.XlWBATemplate.xlWBATWorksheet);
            Microsoft.Office.Interop.Excel.Worksheet worksheet= (Microsoft.Office.Interop.Excel.Worksheet)workbook.Worksheets[1];//取得sheet1
            //寫入標題
            for (int i = 0; i < dgv.ColumnCount; i++)
            {
                worksheet.Cells[1, i + 1] = dgv.Columns[i].HeaderText;
            }
            //寫入數值
            for (int r = 0; r < dgv.Rows.Count; r++)
            {
                for (int j = 0; j < dgv.ColumnCount; j++)
                {
                    worksheet.Cells[r + 2, j + 1] = dgv.Rows[r].Cells[j].Value;
                }
                System.Windows.Forms.Application.DoEvents();
            }
            worksheet.Columns.EntireColumn.AutoFit();//列寬自適應
            MessageBox.Show(fileName + "資料儲存成功", "提示", MessageBoxButtons.OK);
            if (saveFileName != "")
            {
                try
                {
                    workbook.Saved = true;
                    workbook.SaveCopyAs(saveFileName);
                }
                catch(Exception ex)
                {
                    MessageBox.Show("匯出檔案時出錯,檔案可能正被開啟！\n" + ex.Message);
                }
            }
            xlApp.Quit();
            GC.Collect();//強行銷燬
        }
    }
}
 

真正呼叫的時候，用以下程式碼。

        private void btnExcel_Click(object sender, EventArgs e)
        {
            ToExcel frm = new ToExcel();
            frm.RExcel(dataGridView1);
        }