Deformation and failure can easily happen in soft rock roadway of coal mine, and one of the most important features is large deformation of the floor. In order to study the deformation and failure mechanism of roadway in the mud weakly consolidated soft rock strata, the bypass roadway of auxiliary shaft in the new Shanghai No.1 Coal Mine was taken as the engineering background. Through mechanics experiments to rock samples, special physical and mechanical property of surrounding rock were discovered, including low strength, poor cementation, muddying and swelling in the presence of water. Combining the results of situ monitoring and numerical simulation, deformation of floor of roadway was featured with fast speed, lasting long, large total volume and no convergence, and the deformation was large nolinear deformation mainly composed of flowing and swelling. Tendencies of failure and deformation were the same, expanding speed of plastic zone was faster in early stage than later stage, but the zone kept expanding. Through analyzing their mechanism, deformation and failure of the floor in roadway was the result of vicious circle under coupling effect of water and tectonic stress. As the floor heave was of the type which was integrated with flowing and swelling, water controlling and support reinforcing were key measures which were taken to deal with floor heave. Based on the study above, the support scheme of the bypass roadway of auxiliary shaft was optimized and the monitoring data showed that deformation and failure of the roadway were effectively controlled.