Abstract：Two important elementary problems of rock (mass) mechanics are put forward，residual stress in rock mass and rock mechanics theory that embodies unloading characteristics，which needs to be established urgently. The main reason and mechanism about forming residual stress are analyzed，and several examples are presented. The theoretical disadvantage resulting from using the loading theory to calculate unloading problem is demonstrated by a simple example. In the past，the influence of initial stress on calculation result is not considered，and the excavation-induced displacement calculated according to existing theory is much smaller than real one. The smaller the Young¢s modulus is and the bigger the in-situ stress is，the bigger the error of calculated displacement for rock (mass) is.
