Hysteresis motors are used in special applications such as gyroscope and gascentrifuge due to their unique features such as synchronism, self-starting, and developing smooth torque. Dynamic modeling of hysteresis motors is essential to the prediction of the transient performance, the study of the dynamic stability, the development of modern closed-loop control, and the estimation strategies. This paper develops a new time varying Dynamic model for a high-speed, circumferential- flux type hysteresis motor, in which the parameters of equivalent circuit of rotor's material are adjusted based on operational B-H loop. For this purpose and based on the elliptical assumption about B - H loops, the hysteresis lag angle, , is updated due to the applied stator voltage and available load torque. Developed mathematical model satises many theoretical aspects of hysteresis motor behavior in transient and steady-state situations. The model offers a tool to study the start-up of hysteresis motor, the change of stator voltage, the variation of load torque, the frequency tracking of variable-speed applications, and transient-state response to design parameters. Some simulations are provided to demonstrate the validity of developed model in Matlab/Simulink and are veried by some experimental results. The proposed results verify the advantages of this model over previous research works.