Embodiments of the present invention provide a method, a terminal device, a network-side device, and a communications system for managing a power supply. The method includes: determining a terminal power consumption level according to remaining power or terminal settings, where the terminal power consumption level is one of at least two power consumption levels. In the embodiments of the present invention, different power consumption levels are applied according to different remaining power of a terminal power supply or terminal settings, thereby adapting to differentiated power consumption requirements and improving the power supply utilization efficiency of a terminal.