This paper proposes an electromagnetic transient transformer model on account of ferromagnetic hysteresis of its core， which is used to simulate magnetizing inrush currents during no-load transformers switching on. The hysteresis loop of the transformer ferromagnetic core material is built based on the Jiles-Atherton phenomenological model. Comparison is made between the calculated（with suitable parameters） and measured B-H curve and found that good agreement is achieved. By analyzing the core and coil construction of a single-phase three-winding transformer， the electromagnetic transient math model is built. Based on a simplified electrical and magnetic model of the transformer and the duality principle， a three-phase five-legged transformer transient model is constructed. The simulation for magnetizing inrush current of a single-phase three-winding transformer is implemented with MATLAB/Simulink， the results verify the validity of the math model. In addition， magnetizing inrush current has also been simulated for both three-phase transformer and three-phase five-legged transformer. The simulation results demonstrate the validity of the math models and the effectiveness of analyzing the magnetizing inrush current.