The invention discloses an annular space continuous nitrogen injection auxiliary heat insulation method for offshore thermal recovery. The method comprises the following steps that: thermal fluid is injected into a heat-insulating oil pipe; nitrogen is continuously injected into an annular space which is formed between the heat-insulating oil pipe and a sleeve; the nitrogen is converged with the thermal fluid at an output end of the heat-insulating oil pipe; and the nitrogen and the thermal fluid are input to a stratum together. By the method, annular space heat insulation of a heat injection period can be realized, the sleeve is protected, the continuously injected nitrogen simultaneously enters the stratum, the energy of the stratum is increased, the energy increasing and pressure keeping effects are carried out, and meanwhile, the sweep range of the thermal fluid can be improved and the thermal recovery effect is improved.