Abstract: On the basis of Kogelnik model,effects of the ambient temperature on diffraction efficiency are analyzed for potassium lithium tantalite niobate(KLTN) crystal. The diffraction efficiency attains its peak value when the ambient temperature is Curie temperature. A temperature control system is designed to control the ambient temperature of KLTN based on PID algorithm,with the measurement precision of± 0. 3 ℃,and the control accuracy of ± 0. 5 ℃. The variations of the diffraction efficiency with the ambient temperature are measured using two-wave mixing setup,and the experimental result agrees with the one of simulation,and Curie temperature 22. 5 ℃ for KLTN crystal,which is consistent with the one obtained by using resonance method.