Abstract: In order to meet the requirements of component surface micro-topography measurement system for remote transmission and real-time online non-contact measurement, as well as high accuracy, high resolution and high signal-to-noise ratio measurement, we presented an optical-fiber heterodyne method of contour detection based on acousto-optic modulation. We established the mathematical model through the principle analysis, drew the suface roughness measurment block diagram and measured the suface roughness of the testing component with achieving the resolution of 1 nm. Moreover, we discussed the source of uncertainty and control method, the measurement accuracy was 1. Results show that the noise, resolution and measurement can be improved by the fiber-optic hererodyne contour detecting technique based on acoustooptic modulation.