The longitudinal ultrasonic wave launched by ns-laser pulse is used to measure the temperature dependence of the elastic modulus C33 of single crystal sapphire. The result shows that in a temperature from room temperature to 1000 ℃ the elastic modulus of sapphire C33 reduces as the temperature increases, following the relationship C33 = - 1.541 10-5T2 - 0.021T + 498.3. In this method, the ablation mechanism is adopted to launch strong longitudinal waves, therefore, the result is accurate that the error of the measurement is estimated to be no more than 0.1%.