The utility model provides a protecting device for electric generator, including primary loop and secondary circuit, primary loop includes live wire and ground wire, and it has ampere meter and overcurrent relay to establish ties on the live wire, and it has the voltmeter to connect in parallel between live wire and ground wire, secondary circuit includes live wire and zero line, and the main -control circuit that establishes ties between live wire and zero line and have fuse and series mode voltage protect relay's in proper order normally closed contact, overcurrent relay's normally closed contact, separating brake switch, closing switch and auxiliary relay to form has a closing switch pilot lamp in that auxiliary relay's both ends are parallelly connected, at the parallelly connected protect relay 2 who has auxiliary relay in closing switch's both ends, two protect relay 2 of closing switch set up respectively the live wire with on the line, the master control branch road and the voltage protect relay that connect in parallel and have the auxiliary relay's of series connection normally closed contact and separating brake switch pilot lamp to form at main -control circuit's both ends. The utility model discloses play over -current protection to the generator and act on, play the low -voltage protection effect to testing instrument.