The nonlinear phase shift and the changes of fundamental wave amplitude caused by Cherenkov cascading second order nonlinearity have been analyzed and optimized, taking into account the propagation loss. According to author′s calculation, the nonlinear phase shift and the change of fundamental power are strongly dependent on two parameters: the thickness of the waveguide and the fundamental light wavelength. The results show that, a very large nonlinear phase shift (>2π) could be attained with a very small depletion of fundamental power even if the reversal period is not introduced into the waveguide by properly choosing the two parameters, which is very attractive to the realization of the all optical switches. Many useful results are obtained which are important to the research and development of all optical switches.