In this technical note, the rock failure process analysis software RFPA2D was used to reproduce unloading-induced brittle failure. Especially, the approach aims to investigate the mechanism and the failure mode of unloading-induced rock failure. Two tunnel excavation models were built to conduct the numerical simulation. Failure characteristic of a single-stage excavation under unloading exhibits a very brittle failure behavior and a sudden and intense energy release. The predominant failure mode is spalling, further developing some local shear failures, with fractures approximately parallel to the excavation boundary. The failure mode of multiple-stage excavation is predominantly shear failure with some local tensile failures. The energy release rates in a single-stage excavation and multiple-stage excavation are compared simultaneously after the unloading, the total energy and the releasable strain energy for the case of a single-stage excavation are much higher than that for multiple-stage excavation. This note presents the rock failure intensity and the damage mode significantly, with satisfactory results.