The embodiment of the application discloses a test device and method for pulse withstanding interval ratio of insulating oil under VFTO composite overvoltage. A pulse generating system is electricallyconnected to a control system and a test system respectively, the pulse generating system comprises a pulse generating unit, the signal output end of the pulse generating unit is electrically connected to the first ends of a lightning pulse transmission cable and a VFTO pulse transmission cable respectively, the second end of the lightning pulse transmission cable and the second end of the VFTO pulse transmission cable are connected to the first end of a high voltage electrode in the test system; the second end of the high voltage electrode is immersed in insulating oil; a sampling port of adielectric strength tester is connected to a sampling port valve. The control system controls the pulse generating system to generate a lightning pulse and a VFTO pulse which act on the insulating oilin the test system, sample and test the insulating oil under the combined action of the lightning pulse and the VFTO pulse by dielectric strength tester to obtain the pulse withstanding interval ratio under a composite overvoltage, and determine the insulation strength of the insulating oil.