An adaptive polarization conversion system of non-polarization maintaining (PM) fiber amplifier is reported, which can convert any non- PM laser into linear polarized one. The model of adaptive polarization conversion system is established based on the principle of the controller and the mechanism of polarization evolution. The relationship of the output polarization extinction ratio at different conditions is analyzed. On the basis of the optimization results, the system achieves the polarization conversion of non-PM fiber amplifier with the output extinction ratio of 16.7 dB using adaptive polarization conversion technology to control the polarized component directly based on stochastic parallel gradient descent (SPGD) optimization algorithm.