Abstract: For the sake of exploring the law of creep-large deformation of soft rock under high and steep slope in open-pit mine, conventional compression, pre-peak compression creep and post-peak compression creep experiments of soft rock were carried out. The results showed that: the conventional stress-strain curve of soft rock illustrates a clear tendency to transform from elastic-brittle plasticity to elastic-plastic plasticity. This phenomenon is more obvious due to the lower strength of soft rock; soft rock creep strain is more sensitive to confining pressure, which increases from 2.5% to 14.5% at low confining pressure before peak, which indicates that soft rock has typical large deformation characteristics under low confining pressure and high stress; the creep strain of weak soft rock has less change after peak, which indicates that the creep characteristics are unstable in this time; the viscosity coefficient before peak is greatly affected by the confining pressure. As the confining pressure increases, the viscosity coefficients of K-body and M-body gradually decrease; the confining pressure has little effect on the viscosity coefficient after the peak. However, the influence of the K-body viscosity coefficient is greater than that of the M-body, and soft rock with elastic stage will transform to plastic stage. Based on the experimental research, the BNSS creep-large deformation constitutive model of soft rock was established.