The loess - rocky landslide and rock landslide have a wide distribution in Gansu tianshui region, having a large quantity, and the major sliding surface are happened to mudstone. in order to further understand the creep characteristics of soft rock and the nature of landslide deformation and failure, this paper used YSJ-01-00 rock triaxial creep test machine to carry out the triaxial compression creep test the of mudstone in the natural state under multi-stage loading which was obtained in Tianshui, Gansu. And the complete creep curve, different stress level strain-time curves, and long-term strength of mudstone are obtained. The creep behaviors of the mudstone samples are analyzed, a modified Nishihara model and the failure criteria of the model are obtained. The parameters of the modified Nishihara model and the creep damage time are derived by fitting the modified Nishihara model to compression creep curve of the mudstone samples. The results show that the modified Nishihara model can effectively describe mudstone creep, especially in the accelerating creep stage, which is conducive to the research of landslide prediction, and has great scientific significance and engineering significance to the study of loess-rock landslide, rock landslide and other soft rock in Gansu area.