A loading system for a Hopkinson pressure bar test under water-gas-temperature multi-field coupling action includes: a sample sealed cabin which includes sealing flanges, Y-shaped and high-temperature resistant sealing rings, and a sealed cabin body; a gas pressure loading device which includes a high-pressure gas tank, a pressure regulating valve, a second barometer, a second high-pressure valve and a first three-way valve connected in sequence; a water pressure loading device which includes an electric pressure test water pump, a water pressure gauge, an accumulator and a one-way valve connected in sequence; a temperature loading device which includes thermocouple heating rods, a temperature display and a thermocouple temperature control circuit board connected in sequence; and a dynamic and static combined loading device which includes an axial pressure loading device, an impact loading device and a Hopkinson pressure bar member.