<p>The synchronous condenser (SC) must have strong transient reactive power (TRP) characteristics to support the bus voltage in high voltage direct current (HVDC) transmission systems. The leakage magnetic field produced by the end winding is a critical factor that impacts the TRP characteristics of SC. Optimizing the end winding structures is an effective approach to enhancing the TRP characteristics of SC. Consequently, this paper proposes a multi-dimensional field-circuit-machine-network coupling model for SC and quantitatively investigates the impact of the end winding structures on the TRP characteristics of SC. The end leakage magnetic field of different end winding structures is firstly calculated and analyzed, including the tilt angle of the involute part and the extended length of the line part. Furthermore, the end leakage reactance and transient parameters are studied under different end winding structures. On this basis, the TRP responses of SC under different end winding structures are obtained. The impact law and degree of the end winding structures on the TRP characteristics of the SC are revealed. The calculation model is verified through experiments. The conclusions can offer a theoretical foundation for enhancing the TRP characteristics of the next-generation SC.</p>