In order to solve the roadway support problem of weakly cemented soft rock in west China, we collected typical weakly cemented mudstone samples in Luxin coal mine in Inner Mongolia, and conducted indoor triaxial compression test on the soft rock at different states (natural state, saturation state, dry state) under different stress levels. We analyzed the relations of strength characteristics, fundamental mechanical indexes vs. confining pressure. The results are as follows firstly, the peak strength and residual strength of weakly cemented mudstone are very low under natural condition. With the increasing confining pressure, the peak strength and residual strength of mudstone both have a larger increase, and the relationship between peak strength and confining pressure is logarithmic. Secondly, as mudstone is very sensitive to water, peak strength and residual strength decreases with the increasing moisture content, while peak strength decreases more significantly. Thirdly,softening coefficient decreases with the increasing confining pressure, and the elastic moduli of mudstone under three different states increase linearly with the increasing confining pressure. Lastly, we established the triaxial compression stress-strain relationship by analyzing the four-stage triaxial compression stress-strain fitting curve of mudstone.