Based on the Fabry-Perot (F-P) cavity model with three mirrors,the theoretical model of the triple feedback effect of non-alignment cavity was established,numerically simulated and experimentally validated. The factors affecting the power turning properties of the self-mixing interference were analyzed under three conditions:1) double and triple feedback effect of alignment cavity;2) double and triple feedback effect of non-alignment cavity;3) the feedback effects when a λ/4 plate was inserted into the external cavity. The experimental results are in good agreement with theoretical analysis. It is shown that,the resolution of the self-mixing interference system can be up to λ/6;the self-mixing interference signal is related with the reflectance of the cavity mirror,the alignment of the cavity mirror and other plates in the external cavity;the self-mixing interference signal in condition (3) is similar to that of the non-alignment cavity;the information of the displacement direction of the reflector is contained in the self-mixing interference signal of double and triple feedback,so it could be easily distinguished.