A system for line powering includes at least one office-end PSU, one standby PSU and one power switching unit. The office-end PSU provides power for a group of subscriber lines in a centralized manner. The power switching unit monitors the power supply status of the office-end PSU and controls the switching between the office-end PSU and standby PSU. In embodiments of the invention, different rectifier/boost circuits and different step-down circuits need not be set for each pair of subscriber lines between the office-end PSU and the remote device. When an office-end PSU fails to supply power, the standby PSU can be switched over quickly to supply power for the remote device, which cuts down the cost for designing the office-end PSU and the standby PSU while ensuring the reliability of power supply for the remote device.