Abstract: With the development of rail transit in speed and carrying capacity, the train safety problems caused by wheel tread defects and wear have become more prominent. A new method of reconstructing the wheel tread profile based on phase measurement profilometry (PMP) is proposed to detect the wheel tread defects and wear.In this paper, simulation experiments are carried out to compare the four phase unwrapping algorithms of the row and column expansion method, the least square method, the branch cutting method and the improved branch cutting method under different levels of noise. The experimental results show that the improved branch cutting method has the relatively smallest error, strong anti-noise performance and fast operation speed. The effectiveness of the improved method is verified by the reconstruction of the wheel tread and the defective wheel tread profile.