MOST bus protocol is a high speed multimedia transmission protocol which applies to the in-vehicle entertainment system to solve wiring difficulty, EMI and so on. However, with the increasing number and complexity of the in-vehicle entertainment devices, the energy consumption of system grows continuously. In the paper, a kind of the centralized power management based on the MOST networks is designed. The PowerMaster function in the MOST Master node can control and change the status of every device node by monitoring the running situation of the whole MOST networks. At last, the experiment indicates that the PowerMaster can manage the power supply of the MOST networks effectively. Under the control of the PowerMaster, the system energy cost is lower than before.