Fiber point diffraction interferometer meets the accuracy of optical test for extreme ultraviolet lithography (EUVL). Wavefront reference source which emits circularly polarization state light can enhance the contrast of interference fringes and reduce the astigmation of wavefront reference source. The principle of phase-controlled polarization controller is analyzed by Mueller matrix and found to obtain circularly polarization by only using the first two control channels. A polarization control system has been designed, and the light intensity is analyzed after propagating from the polarization control system by Jones matrix. The control voltage of the first two control channels are obtained. A polarization control system is built and a circularly polarization light is achieved. The error between theory and reality is about 7.5%, which is verified by analyzing the first two control channel before polarization control test. The polarization of wavefront reference source is controlled into circularly polarization quickly, thus the problem of polarization control is solved for fiber diffraction interferometer.