A novel method to adaptively convert laser beam from non-polarized to linearly polarized based on the principle of polarization phase locking is presented. The non-polarization laser is divided into two beams whose polarization states are perpendicular to each other by a polarization splitter. Based on the principle of coherent polarization beam combining, and used the phase modulator whose operating voltage is optimized by parallel gradient descent algorithm to keep the difference of phase of the two splitter beams to mπ. The output beam is linearly polarized laser with high polarization extinction ratio. In theory, the model of adaptive polarization conversion is built, and the factors affecting the efficiency and polarization extinction ratio are analyzed. In experiment, experiment system is built based on the optical path of free- space structure, and the adaptive conversion of non-polarization maintaining laser to a linearly one with the polarization extinction ratio of 93.5% and the converting efficiency of 88% is realized.