A continuous flow micro-channel reactor was used to selectively remove methyldichlorosilane from trichlorosilane by photochlorination reaction. The effect of various factors on the removal rate of methyldichlorosilane was investigated. The results show that increasing the chlorine gas and light intensity, increasing the reaction temperature, reducing the wavelength of the light source, and prolonging the reaction time are beneficial to the removal of methyldichlorosilane. Under the optimal conditions, the methyldichlorosilane content in the product is less than 0.05ppm, the removal rate reached to 99.6%. A small amount of silicon tetrachloride is found in the reaction products, which is formed by chlorination of polychlorosilane and trichlorosilane. With the improved trichlorosilane as the raw material, the carbon content of the polycrystalline silicon prepared by the evaluating furnace is less than 3?1015atoms/cm3,which meets the requirements of the first-grade electronic products.