The invention discloses an efficient supercritical nuclear power system and a working method. The system comprises a water condensation system with a low-temperature flue gas waste heat utilization device, a water supply system with a medium-temperature flue gas waste heat utilization device, a turbine high-pressure cylinder for coupling, a turbine low-pressure cylinder for coupling, a non-nuclearfuel energy release and conversion device and a nuclear island. The output of the water condensation system with the low-temperature flue gas waste heat utilization device is sequentially connected with a high-pressure water supply pump, a first high-pressure heater and the medium-temperature flue gas waste heat utilization device, the output of the medium-temperature flue gas waste heat utilization device is divided into two paths, one path is connected with the non-nuclear fuel energy release and conversion device, the other path is connected with a water supply inlet pipeline of the nuclear island, an outlet steam pipeline of the nuclear island is divided into two paths, one path is connected with the non-nuclear fuel energy release and conversion device, and the other path is connected with the turbine low-pressure cylinder for coupling. The technological parameter characteristics of existing mature nuclear islands and non-nuclear-fuel boilers are sufficiently utilized, and the problem that equipment manufacturing is difficult in previous schemes is solved.