Evidence has been accumulating that some massive stars experience enhanced mass loss shortly before the explosion. The physical mechanisms for this mass loss is not clear, and several ideas have been proposed, including gravity waves generated in the convective core (Quataert & Shiode 2012) or binary interaction (Chevalier 2012). In my research, I investigate the effect of continuous energy deposition in the envelope which is injected artificially on the envelope's dynamical behavior and mass loss. I have found that depending on the  energy injection rate there are three possibilities. One is that the envelope expands quasi-hydrostatically. Second, the envelope oscillates radially and amplifies, culminating in partial mass loss. Third possibility is the whole envelope ejection at once. In this presentation, I will explain these results and its implications in the context of pre-SN mass loss.