Abstract: The average corrosion rate of aluminum alloy cladding directly reflects the corrosion resistance of the cladding material in research reactor. The operating experience of the high flux engineering test reactor（HFETR） shows that a large amount of radionuclide ²⁴Na will be produced in the primary circuit by the activation corrosion of aluminum alloy cladding,and the activity concentration of radionuclide ²⁴Na reached an equilibrium value rapidly. The ²⁴Na nuclide produced by aluminum alloy cladding in the HFETR is the main source of the activity concentration of the primary circuit. Theoretically, the average corrosion rate of aluminum alloy cladding can be quantitatively evaluated according to the ²⁴Na equilibrium activity concentration in the primary circuit of HFETR. Based on the analysis of the formation, release and migration mechanism of ²⁴Na nuclide in the primary circuit of HFETR, the primary circuit is divided into three zones: irradiation zone, coolant zone and purification zone. The three-zone transport model between the average corrosion rate and the equilibrium activity concentration of ²⁴Na is established. Then the Monte Carlo Nuclear Particle Transport Program（MCNP5） is used to calculate the required physical parameters in the model. Finally, the average corrosion rate of three kinds of aluminum alloy cladding with three different materials or surface pretreatment process is evaluated and calculated by using the operation monitoring value of ²⁴Na activity concentration in the primary circuit of HFETR, and the results are compared with the results of out-of-reactor corrosion test. The comparison shows that the method proposed in this paper can accurately and quantitatively evaluate the average corrosion rate of the aluminum alloy cladding in the reactor, and can provide an analysis basis for studying the actual corrosion resistance of the aluminum alloy cladding for the research reactor.