具体的我也不清楚为什么,我只能把我可以用的代码贴给你：
Application ExApp;
Workbook Xbook;
Worksheet XSheet;
/// <summary>
/// winapi 用于找到句柄线程
/// </summary>
/// <param name="hwnd"></param>
/// <param name="ID"></param>
/// <returns></returns>
[DllImport("User32.dll", CharSet = CharSet.Auto)]
public static extern int GetWindowThreadProcessId(IntPtr hwnd, out int ID)
//关闭和销毁
public override void Close()
{
ExApp.Quit();
System.Runtime.InteropServices.Marshal.ReleaseComObject(XSheet);
System.Runtime.InteropServices.Marshal.ReleaseComObject(Xbook);
//调用window api查找Excel进程,并用关闭
IntPtr t = new IntPtr(ExApp.Hwnd);
int ProcessById;
GetWindowThreadProcessId(t, out ProcessById);
System.Diagnostics.Process ExcelProcess = System.Diagnostics.Process.GetProcessById(ProcessById);
ExcelProcess.Kill();
XSheet = null;
Xbook = null;
ExApp = null;
}