The invention discloses a preparation method of a temperature-resistant and salt-resistant soluble multi-component copolymer: (1) Mixing a temperature-resistant water-soluble polymer solution and a photoinitiator solution, adding a water-soluble monomer, mixing, passing an inert gas to remove oxygen , and then placed under ultraviolet light for 10 to 30 minutes, and the light intensity was set to 500 to 10000 μW / cm 2 ; That is, a temperature-resistant multifunctional macromolecular initiator; (2) Dissolving the temperature-resistant multifunctional macromolecular initiator in water, then adding monomers, passing an inert gas to remove oxygen; Living / controllable radical polymerization of water-soluble monomers to obtain temperature-resistant and salt-resistant multi-polymers. The temperature-resistant and salt-resistant multi-component copolymer of the present invention has an ultra-high molecular weight of 1.9×10 7 Above, and temperature-resistant, salt-resistant, it can be used to increase the viscosity of aqueous solution under high-temperature and high-salinity conditions, and can be used as an oil displacement agent for tertiary oil recovery under high-temperature and high-salinity geological conditions to enhance oil recovery.