Seismicity as an important parameter in a mine indicates rock damage, which is widely used for prediction and control of the stability of surrounding rock mass during mining. To investigate failure mechanisms of surrounding rock during mining, we propose solutions to key issues concerning applications of the moment tensor theory. A moment tensor three-component decomposition model is introduced to solve the uncertainty of the solution of equations of moment tensor decomposition due to the uncertainty of mining-induced stress states. The deficiencies of the criterion of rock failure modes proposed by Ohstu are discussed and thereby a revised criterion is proposed to analyse rock failure modes in a mine. Failure mechanisms of surrounding rocks in Dongguashan Cooper Mine are studied by the proposed seismic moment tensor method. The results show that the major rock failure of Dongguashan roadway is shear failure, in combination with the failure mode of the combined action of multiple factors. When tunnels are located in different rock contact zones, microseismic events cluster in the contact zone and a shear band occurs in the seismic event clustered area. However, when tunnels are located in one stratum, the distribution of microseismic events is more dispersed. The failure is caused by the stress concentration, and the failure mode is the local surrounding rock caving.