Abstract: By using a slope on standard sample, an improved method about calibration of tip torsion coefficient on friction force microscope was proposed. Based on forces exerted on the slope during sliding, the half-height and offset of friction-loop on slope was measured under different loads. Then the friction coefficient could be solved and the torsion coefficient could be calculated. Results show that the half-height and offset of friction-loop on slope increased linearly under higher load range. On this basis, solving of friction coefficient and torsion coefficient was independent on the adhesion force. After calibration, the verifying tests on flat suggested that the measured friction coefficient was similar to the solved one. These results may be beneficial to the calibration and measurement of friction force in nanoscale.