重载DefWindowProc()函数，过滤WM_NCLBUTTONDBLCLK在HTCAPTION区的响应即可：

#define   WM_NCLBUTTONDBLCLK   0x00A3
LRESULT CMainFrame::DefWindowProc(UINT message, WPARAM wParam, LPARAM lParam) 
{
// TODO: Add your specialized code here and/or call the base class
switch(message)
{
case WM_NCLBUTTONDBLCLK: 
if(HTCAPTION==wParam) 
{ 
return 0; 
}
}
 return CFrameWnd::DefWindowProc(message, wParam, lParam);
}