Abstract: Renewed inferences and calculations have been made on the calculating formula for sliding friction coefficient with MM 200 friction and wear tester. Compared with the previous calculating formula for the sliding friction coefficient,the currently inferred one has a relatively small calculating error.This error increases with the increase of the rim angle between the ring and block specimens.Subsequently the reliability and comparability of the experimental data could be decreased greatly. Therefore it is suggested that the currently inferred calculating formula be used for calculation of the friction coefficient with MM 200 tester.