The invention discloses a preparation method of a heat-resistance salt-tolerance water-soluble multipolymer. The method comprises the steps that 1, a heat-resistance water-soluble polymer solution ismixed with a photoinitiator solution, a water-soluble monomer is added, the mixed solution is evenly mixed, inert gas is introduced to the mixed solution for oxygen removal, then the mixed solution isplaced under ultraviolet light for radiation for 10-30 minutes, and the light intensity is set to be 500-10,000 muW/cm<2>, so that a heat-resistance polyfunctionality macroinitiator is obtained; 2, the heat-resistance polyfunctionality macroinitiator is dissolved in water, then the monomer is added, and inert gas is introduced to the mixed solution for oxygen removal; then, by adopting a thermalinitiation mode, the water-soluble monomer activity/controllable free radical polymerization is initiated, and accordingly the heat-resistance salt-tolerance water-soluble multipolymer is obtained. The heat-resistance salt-tolerance water-soluble multipolymer has super-high molecular weight above 1.9*10<7>, is resistant to temperature and tolerant to salt and can be applied to aqueous solution tackifying under the high-temperature and high-salinity condition and used as a tertiary oil recovery oil displacement agent under the high-temperature and high-salinity geological condition, so that thecrude oil recovery factor is increased.