Plane transformers are vital components of high-frequency power electronic converters, and the calculation and optimal design of their parallel winding losses pose significant challenges in the design process. This article proposes a theoretical calculation method for winding losses based on impedance matrix and circuit equations, and it derives the significance and acquisition methods of impedance matrix parameters under high-frequency conditions. Building upon the proposed theoretical calculation method for winding losses, the article performs classification analysis of circuit equations to determine the constraints of the optimization problem. It establishes a mathematical model for optimizing winding losses in a single topology and provides a general solution method for designing the optimal structure of winding losses. Finally, experimental measurements are conducted to validate the effectiveness of the optimization method presented in this article.