Mechanical energy may initiate and accelerate chemical reaction in chemical mechanical polishing (CMP). To study the effect of mechanical energy on the chemical reactions, a special friction measuring system was designed in this paper. The system could measure the local friction to reduce the error caused by resultant force. The effects of rotational speed, polishing pressure and the concentration of oxidant on friction and material removal rate were investigated. The results showed that the system could accurately measure the friction of small area diamond film in CMP process. The frictional system was in a mixed lubrication state since the value of the friction coefficient located in the range of 0.060~0.065.