Based on the analysis of the theory model of self-mixing interference (SMI) with two feedback external cavity structure, the processing method of self-mixing interference signal is analyzed and simulated. Under the weak feedback level, the reconstruction of synthetic signal phase and the shape reconstruction of two channel signals of external cavity are realized by using the Hilbert transform, and the maximum error is less than 1.5 rad. The self-mixing interference signal with noise is preprocessed by the wavelet soft threshold and ensemble empirical mode decomposition (EEMD) combining algorithm, which achieves a good effect.