The bulk elastic modulus represents the anti-compression capacity of the transmission fluid,and its dynamic change will affect the precise regulation on transmission system.Taking ISO 4113 test oil containing air and steam as the research object,a homogeneous flow model and a dynamic model for the bulk modulus of elasticity in the transmission pipe were established.Considering the temperature change and cavitation effects (air cavitation,steam cavitation,and pseudo-cavitation) caused by the compression of transmission fluid,based on Roe scheme decomposition and Steger Warming flux splitting method,a new numerical solution method was proposed to predict the changes of pressure and void fraction in different cavitation zones,and the spatiotemporal evolution of bulk elastic modulus was predicted.The effects of pressure,void fraction,and temperature on the dynamic bulk modulus were discussed,and the differences between the two models were compared.The results show that in the low-pressure region,the prediction results of the dynamic bulk elastic modulus of the two models are basically consistent; when the pressure is less than 1 MPa,the dynamic bulk elastic modulus increases with the increase of pressure and decreases with the increase of the initial void fraction,while the effect of initial temperature is not obvious; when the pressure is within 1 MPa to 10 MPa,the dynamic bulk elastic modulus increases rapidly with the increase of pressure,decreases with the increase of initial void fraction and temperature,and its change rate decreases continuously; when the initial void fraction is less than 5%,the dynamic bulk elastic modulus-pressure curve predicted by the dynamic model is smoother; when the pressure is greater than 10 MPa,in the homogeneous flow model,the dynamic bulk elastic modulus increases linearly and slowly with the increase of pressure,while in the dynamic model,the dynamic bulk elastic modulus tends to be stable with the increase of pressure due to the continuous dissolution of gas.The comparison shows that the homogeneous flow model is suitable for low pressure, and the dynamic model is also suitable for high pressure.