The diamond films adherent to Si substrate are deposited with the microwave plasma CVD (MPCVD) at microwave powers of 6000 W and 4000 W from 6 h to 10 h, respectively, the internal stresses of the films are measured by XRD. Spectral peak shift and widening are applied to calculate the magnitudes of macro and micro stresses. The results show that the macro stress is tensile. The internal stress can be controlled by the microwave power. With the microwave power increasing, the intrinsic and macro stresses decrease, and the micro stress increases significantly. Also, it can be found that the macro and micro stresses increase with deposited time when the other conditions are the same. This work has been supported by the National Natural Science Foundation of China(No.60576011), Key Laboratory Foundation of Tianjin(No. 06TXTJJC14701), and Colleges and Universities Foundation of Tianjin(No. 20050519).