Abstract: The disclosure relates to the field of nuclear power energy technology, and specifically relates to a screening method for an optimal zinc ion concentration in the primary loop during the hot functional test of a nuclear power plant. Unlike the study of zinc injection in primary loop during pre-critical and power operation of a nuclear power plant, the disclosure is directed to the study of optimal zinc injection concentration during the hot functional test. Specifically, in the disclosure, a hot functional test environment is simulated by an autoclave, and the optimal zinc ion concentration range is identified by impedance experiments on test specimens with film formation in the autoclave. The method is highly representative of tests, with clear data trends, high experimental visibility and evaluability, which provides a screening method for the optimal zinc ion concentration in the primary loop during the hot functional test of a nuclear power plant.