Abstract: A method of two-step surface pretreatment utilizing two kinds of solutions to etch respectively the surface WC and Co in cemented carbide substrates was investigated. Diamond films were deposited by means of the High Current Extended DC Arc Plasma CVD Equipment. The results showed that the two-step method can effectively remove the Co in cemented carbide substrates and obviously roughened the surface of the cemented carbide. Enhancements both on the quality and adhesion of the diamond coatings were observed.