This paper proposes a new method of phase unwrapping based on auxiliary light, which is used to break the limitation of traditional phase unwrapping algorithm and expand the measurement range of phase signal. First, based on the wrapped statistical phase in coherent detection based phase optical time domain reflectometer, the wrapped differential phase the reference position and the subsequent position can be solved. Then, based on the joint pulse sequence, the wrapped differential phase is unwrapped according to the traditional phase unwrapping algorithm, and the phase change curves retrieved from the unwrapped differential phases are superimposed together. The position of fiber that correctly implements the traditional phase unwrapping algorithm can be obtained from the linear feature of the superimposed phase change curve. Therefore, the phase signal corresponding to the disturbance source can be correctly obtained based on this linear feature of phase change. In the experiment, a phase signal with a maximum absolute phase difference of 3.7154 between adjacent sampling points can be perfectly reconstructed.