Abstract：In order to analyze surrounding rock stability of long alignment high overburden diversion tunnel，conventional triaxial compression tests，unloading confining pressure tests at the pre-peak and post-peak and unloading tests under high groundwater pressure on marble，sandstone and slate are conducted. Systematic contrastive studies are made on the strength and displacement in the experiment. The experimental results indicate that unloading confining pressure has important effect on the intensity of rock. The cohesion and angle of internal friction of rock reduce considerably after unloading confining pressure；the reduction is more obvious especially with water pressure. The effect of unloading confining pressure on cohesion is more obvious than that of angle of internal friction. The reduction extent of cohesion is bigger than angle of internal friction after unloading confining pressure. The effect on rock strength at the pre-peak unloading confining pressure is bigger than that at post-peak unloading confining pressure. The confining pressure of rock failure with unloading confining pressure at the pre-peak is higher than at post-peak；the effect on rock strength unloading confining pressure with water pressure is bigger than unloading confining pressure without water pressure. By unloading confining pressure with water pressure，it can weaken the effect of confining pressure on rock，which makes rock failure with higher confining pressure than that without water pressure.
