Abstract: The correspondence between Leeb hardness and Brinell hardness of 42CrMo4 alloy steel for wind turbine main shafts was obtained using hardness testing methods. The experimental data were analyzed using linear regression, quadratic nonlinear regression, and logarithmic regression, with different conversion formulas compared. The results show that the quadratic nonlinear regression formula provided the best fit for the data. Through formula conversion, Brinell hardness of 42CrMo4 alloy steel could be accurately predicted, demonstrated practical significance for engineering applications.