This study focuses on the transcendental equation with multiple unknowns for determining hydrogeological parameters in an anisotropic aquifer that cannot be directly determined through the conventional analytical methods. The existing methods for solving the equations, including the standard curve comparison method, linear graphic method, and improved linear analytical method, encounter many personal errors, a restricted application scope, and a burdensome and complicated computational process. In this study, adopting the optimum fitting method, a calculation formula for directly determining parameters was constructed using a simple function replacing the well function with a series expansion within the range of engineering adaptive parameters and a drawdown ratio relationship obtained through six selected points on the drawdown curves in three observation holes. The solution of the calculation formula is simple, intuitive, and easy to use. Precision analysis indicates that the maximum error is less than 2% across the range of engineering adaptive parameters, fully meeting the requirements of actual engineering calculation precision.