Abstract: Objective: When transition curve superelevation varies along with slope, conventional methods for calculating transition curve shield center coordinates are insufficient. Additionally, the fitting accuracy of such transition curve shield center coordinates using cubic parabolas often fails to meet design requirements as well. Therefore, it is necessary to investigate the calculation of shield center planar coordinates and curve fitting methods for transition curves with variable superelevation slopes. Method: An equivalent transition curve model is constructed based on the transition curve with variable superelevation slopes. Virtual curve segment track superelevation values are set for calculating the shield center offset planar coordinates at any point on the curve segment. The accuracy of curve fitting is improved by optimizing existing models for shield center curve fitting, ensuring compliance with design requirements. The coefficient of determination is introduced to accurately evaluate the accuracy of the fitting curve equation. The goodness of fit for the transition curve shield center coordinate fitting equation with variable superelevation slopes is determined, and the corresponding goodness of fit intervals are provided. The fitting equation is optimized using the example of Shanghai Rail Transit Chongming Line. Result & Conclusion: The shield center coordinates at any point on the transition curve with variable superelevation slopes can be accurately calculated using the equivalent transition curve. Increasing the fitting order appropriately can better meet the design requirements for fitting accuracy.