The invention discloses a substation line protection non-power-off maintenance device and method. The device comprises a second line protection measurement and control device, a power supply module for providing power for the second line protection measurement and control device, a change-over switch QK1 and a change-over switch QK2. Contacts 2, 6, 10 and 14 of the change-over switch QK1 are respectively connected with a first test line; contacts 3, 6 and 9 of the change-over switch QK1 are electrically connected with three current input ends of the second line protection measurement and control device respectively; a contact 16 of the change-over switch QK1 is electrically connected with the ground end of the second line protection measurement and control device; and contacts 1, 5, 9 and 13 of the change-over switch QK1 are respectively connected with a second test line. When a line protection measurement and control device in a substation needs maintenance, another line protection measurement and control device is utilized to replace the original line protection measurement and control device to work, so that substation does not need to cut off power, and power use of users is not influenced.