Abstract: It is very important to get the value of rock cohesion and internal friction angle, besides, the measured value's credibility is also worthy of our attention. So, by taking several groups of specimens of normal force σ and tangential force τ which arrive at ultimate failure state, we establish simple linear regression equation about σ and τ to test the regression equation, and compile corresponding program to get best solution of φ and c, and carry out further test of regression equation. At last, we found that when significance level α≥0.005, there is a linear relationship between σ and τ; when significance level α≤0.001, there is linear relationship. The results show that the φ, c values are under certain credibility. Therefore we must choose the most appropriate credibility in order to get the best φ, c values.