In ZnS waveguide thin film, using the possitively mode-looked ps (aser beam and light wave coupler, phase matching between foundamental mode TE3(ω) and second harmonic mode TE3(2ω) has been obtained and third harmonic spectra was also observed. The width of the spectral curve were 1.3 and 1.4? respectively. The conversion efficiency of second harmonic is 1.8×10-3 while the incident foundamental power is 20 MW.