Specific discharge is a critical parameter in coal mine hydrogeology. Traditional calculation method usually employs least squares to fit the water yield-drawdown (Q-S) curve, obtaining water yield at the drawdown of 10 meters, followed by well diameter conversion to obtain the specific discharge in standard conditions. However, this method could lead to significant deviations due to its inaccurate discrimination of curve types, failure of some models to pass through the origin, and incomparability of goodness of fit among different models. This study therefore analyzed and optimized the calculation process through a curve selection method based on the coefficient of determination under a unified scale, aiming for more accurate parameters and more appropriate Q-S curves derived via the least squares method. The curvature method was employed as a standard for testing pumping data. We improved the algorithm for the parameters of power function model and the parabolic model, constrained the coefficient of the linear term to be non-negative in the parabolic model, and revised the formula of the logarithmic model. In well diameter conversion, we compared and evaluated the impact of well diameter on the differences of varying methods. This study thus proposes a more accurate calculation process for specific discharge to provide technical support for coal mine hydrogeological work.