This study proposes a fine-grain-mode transition method for variable stages pipeline (VSP) processor. The method is based on dynamic memory access analysing and it reduces energy consumption. A VSP processor varies the pipeline depth dynamically according to workload. When the workload is heavy, the processor shifts into a high-speed mode that drives a deep pipeline at a high clock frequency. When the workload is light, the processor shifts into a low-energy mode that unifies pipeline stages to make the pipeline shallower and drives it at a low clock frequency. The conventional mode transition method cannot follow sharp workload changes because it takes a long time to predict workload. The fine-grain pipeline depth control, this study proposes, is based on a high-speed workload prediction mechanism using memory access frequency, and it uses a novel method to conceal the overhead because of changing the pipeline depth. Simulation results show that the authors approach can reduce the energy-delay product 10% below what it would be with the conventional approach.