Measurement of surface profile can evaluate the smoothness of components. In order to implement measurement with high precision, it comes up with methods for surface-profile measurement, which are the electricdirect modulation for laser-beam frequency and the heterodyne coherence. Through the principle of differential Doppler measurement, we can achieve the digital measurement and optical compensation. Through the technology of electric-direct modulation for laser-beam frequency, we can reduce the size of system and cost. Besides, the transmission by optical fiber has improved the ability of immunity. At the same time, it can improve the resolution by amplifying and tracking the signal measurement. By debugging the circuit, it provides a compensation for the error analysis. The experimental results show that the measurement uncertainty of the technology is less than 0.1%.