Abstract: Using MTS testing machine, the triaxial compression test with four different confining pressures and the uniaxial compression test are carried out on the red mudstone of Badong formation. The complete stress-strain curves of five different confining pressures are obtained. According to the results, the complete stress-strain curve is divided into four main phases. The relationships of the yield strength, the peak strength, and the residual strength with confining pressure are analyzed, respectively. The results show that they get a linear increase relationship with the confining pressure. Also, the bilinear elastic-linear strain softening-residual ideal plastic model is found for the mudstone. The constitutive model of each part is discussed. The related parameters are calculated.