Optical effects in intersectional silicon waveguide switch are investigated by using beam propagation method. The results show that the optical tunneling effect caused by the surface declining wave and leaky wave heavily influences the switching characteristics. There is a strong dependence of reflection power upon the interface position of reflection region, which originates from Goos-Haenschen shift. By restraining the optical tunneling effect and fitting Goos-Haenchen shift, excellent optical switching can be achieved at a very small refractive index change.