Light feedback of external cavity and movement of external cavity mirror in self-mixing interference affect laser frequency. Light fields out of front and rear facets on internal cavity, frequency shift of laser and frequency of self-mixing interference signal are introduced from a model of complex resonant cavity. Frequency shift of laser and frequency spectra of self-mixing interference signal are observed in experiment. Frequency shift of laser is made up resonance frequency shift and movement frequency shift. At lower moving frequency of external cavity mirror, frequency shift of laser out of the front and rear facets are almost the same as resonance frequency shift. At higher moving frequency of external cavity mirror, frequency shift of laser out of the front and rear facets are different from each other. Frequency shift of laser out of the front facet may be dominated by movement frequency shift. Frequency of self-mixing interference signals at extremely weak feedback light is the same as Doppler frequency shift of feedback light. Frequency of self-mixing interference signal at weak feedback light vibrates sharply and its highest frequency is more than 1.6 times of Doppler frequency shift of feedback light.