At the scene of the laboratory simulation industry, an online detection system for the measurement of silicon rod diameter in polycrystalline silicon reduction furnace is proposed. The method of binocular stereo vision is used in the system. Firstly, double CCD is used to get real-time image of silicon rod model, calibration of the camera, extraction of the characteristic points, stereo matching in turn, then the diameter of silicon rod model is calculated through three-dimensional coordinates of feature points. The experimental results show that, silicon rod diameter measurement results achieved the required precision of reduction furnace process parameter automatic control, and the proposed system effectively avoided several factors such as artificial observation for a long time and errors due to subjective factor.