As an example of push-pull SPWM inverter, this paper presents a mathematical model of the push-pull transformer, considers the on-off status of switching devices and discusses the time and space characteristics of the dynamic and effective leakage inductance, which means that the leakage inductance within primary/secondary windings of the push-pull transformer has the action time and associated coil in the different situations. Moreover, it clarifies the relationship among the action time, associated coil and the direction of the energy flow within windings. The simulation results are verified by comparison with mathematical analysis. Experimental measurements show a close agreement with the simulation results as well.