In this paper, we propose a novel method of multi-beam laser heterodyne measurement for small angle based on sinusoidal modulation of simple harmonic motion oscillating mirror. By using the Doppler effect and heterodyne technology, by loading the information about small angle into the frequency difference of the multi-beam laser heterodyne signal, by using the frequency modulation of the oscillating mirror, this method can give many values of small angle after the multi-beam laser heterodyne signal demodulation simultaneously. Processing these values by weighted-average, small angle can be obtained accurately. This novel method is used to simulate measurement for small angle by MATLAB, the obtained result shows that the relative measurement error of this method is just 0.789677%.