Vector polarization mode switch mechanism of the vertical-cavity surface-emitting laser with anisotropic optical injection is numerically investigated. The results are as follows:First, when the injection current is near the threshold current, the polarization state of the VCSEL output is determined by the power of each polarization mode of the optical feedback injection,which is controlled by the external parameter of the VCSEL and the polarizer. Second, the polarization state of the VCSEL output induced by anisotropic optical feedback injection under the controll of polarizer changes periodically. Third, the x^-polarization mode competes drastically with the y^_polarization mode when the power of the x^-polarization of the feedback injection is equivalent to that of the y^_polarization, which induces slight external disturbance of the laser to break the balance of two competing polarization modes. So, on this condition, the polarization state is sensitive to the external parameter change. At last，the y^_polarization mode obtains enough big gain when the injection current is much higher above the threshold current. At this time, the output of the VCSEL is in steady y^_polarization mode. In other words, the polarization state of the VCSEL output is now independent of other parameters.