In this paper, an improved static Jiles-Atherton (J-A) hysteresis model is proposed to simulate the hysteresis properties of soft magnetic composites (SMC) by introducing an excitation factor to control the rotational component of magnetic domains in the effective magnetic field based on the internal demagnetization effect and magnetization mechanism. On the other hand, Since SMC is usually applied in the mid-frequency band, an improved dynamic hysteresis model is necessary to be proposed. The analytical expression for calculating the intraparticle eddy current loss is proposed based on the microstructural parameters of the SMC. And the microstructural parameters are determined by discrete element method DEM. For the intraparticle eddy current loss, the squared term of the mean particle size in the expression is further clarified. Eventually, this improved dynamic J-A hysteresis model was derived through the theory of magnetic field separation. The results show that SMC hysteresis loops with magnetic flux densities up to 1.5 T and frequencies up to 1 kHz can be evaluated by the proposed model.