In order to obtain influence parameters of second-harmonic wave (SHW) conversion efficiency for negative-index materials (NIM) of SHW and positive-index materials of fundamental frequency wave (FFW),the rigorous formulation of SHW conversion efficiency had been deduced on the basis of the coupled-wave equations under the conditions of taking account of walk-off effect,phase mismatching capacity,and the approximation of slow-varying amplitudes for plane wave. The effects of phase mismatching capacity (PMC),intensity of FFW,and walk-off angle of SHW were researched by numerical simulation respectively. Results showed that the conversion efficiency of SHW (CESHW) gradually increased via increasing the intensity of FFW and that the CESHW gradually decreased via increasing walk-off angle and phase mismatching capacity when the intensity of FFW were very small. However,when the intensity of FFW was much large,the CESHW would become obviously periodic evolution via increasing the intensity of FFW. This research would provide a basis for investigating nonlinear theory of negative-index materials. Besides,the length of NIM plays the same as the intensity of FFW in the process of SHW conversion.