Abstract: In order to measure the displacement under the condition of moderate optical feedback self-mixing interference,a displacement measurement method based on phase unwrapping was introduced. Firstly,the system parameters C and α were measured respectively. Secondly,the external cavity phase with optical feedback was recovered after finding the special points of self-mixing interference signal,namely the peak,valley and transition points. Finally,the displacement information of the external moving object was obtained after processing the external cavity phase. Simulation and experimental results proved its feasibility. Experiment results show that the error of the system is ±30nm within the oscillating displacement up to 10 μm. This method is helpful for high precision measurement of micro displacement and vibration.