As a lecture on the research achievements in the past, the authors review the evolutionary process of the rock mass pressure theory and the progress in the researches on the failure mechanism of tunnel. Through model experiment and FEM strength reduction, the failure mechanism can be drawn that the failure of shallowcovered arched tunnel happens on the arch top and the failure of deepcovered tunnel happens on the sidewall, and the location and state of failure surface of rock mass can be worked out.Then, the authors study the change of failure mechanism of rectangular tunnel and arched tunnel. The failure of rectangular tunnel can be divided into three stages: failure on the top of shallowcovered tunnel, failure on the pressure arch of deepcovered tunnel and failure of both sides of deepcovered tunnel. There is no failure stage of pressure arch in arched tunnel.