pd3dDevice->SetClipPlane(0, (float*)f); pd3dDevice->SetRenderState(D3DRS_CLIPPLANEENABLE, D3DCLIPPLANE0 ); for example, f[4] = {0,1,0,0}; it's ok to clip all vertexs below plane y=0; but I want to clip vertexs Above the plane y=0; how to do it ????

It should be as simple as negating the plane's normal:

f[4] = {0, -1, 0, 0};