在子窗体中继承一下列函数即可:
void __fastcall CreateParams(TCreateParams& Params)
{
TForm::CreateParams(Params);
Params.Style = WS_CHILD | WS_CLIPSIBLINGS;
Params.WndParent = Parent_hWnd->Handle;//父窗体的句柄
Params.X = 0;
Params.Y = 0;
Params.Width = ParentWnd->->ClientRect.Right;
Params.Height = ParentWnd->ClientRect.Bottom;
Color = (TColor)0x00E7EBEF;
}