Abstract: To deal with the problem that notable light water reactor decay heat calculation standard is not suitable for fast reactor, decay heat calculation methods were investigated in the paper, including calorimetric method and the summation method, and decay heat experiment about ²³⁵U thermal neutron fission and fast neutron fission from literature. Based on summation method, the calculation method and calculation process of decay heat of ²³⁵U fast neutron fission were proposed, and the relationship between the β-ray decay heat, the γ-ray decay heat and the total decay heat with the decay time after ²³⁵U fast neutron fission were calculated, respectively. The calculated results were compared with the experimental data of ²³⁵U fast neutron fission decay heat. The calculation results show that the calculated decay heat after ²³⁵U fast neutron fission is in good agreement with the experimental results. The maximum relative deviation between the calculated value of the β-ray decay heat and the experimental value is 4.17%. The maximum relative deviation between the calculated value of γ-ray decay heat and the experimental value is 6.78%. The maximum relative deviation between the calculated value of total decay heat and the experimental value is 5.40%. The results of this research have great application potential in the calculation of decay heat of sodium-cooled fast reactor, lead-cooled fast reactor and gas-cooled fast reactor.