The invention provides a spent fuel pool underwater laser soldering testing device and method. The device comprises a simulating pool device (1), a laser device (2), a water cooling tank (3), a controlling device (4), a pressurizing device (5) and an underwater laser soldering moving positioning device (6). The spent fuel pool underwater laser soldering testing device has the advantages that the structure is simple, the operation is convenient, the testing cost is low, soldering working conditions of different water depths can be simulated; an underwater soldering head is completely arranged in water, and the testing device can be used for guiding the producing of an underwater laser soldering technology of an engineering project; a modular design is adopted by the testing device, the testing device can be used for the laser remediation soldering of the bottom plate of the spent fuel pool, and the problems of short effective period, inconvenient construction and the like caused by original countermeasures of temporarily blocking and the like are solved.