Abstract: The hydrodynamic lubrication of a newly developed adaptive structure journal bearing with coupling two step films has been analyzed theoretically. The Reynolds equation and flow balance equation have been solved simultaneously by means of finite differential method in intercrossing iterative numerical calculations. Based on the analysis of the mechanism of film pressure formation and the steady hydrodynamic performance of the bearing, the dynamic coefficients of the bearing have been calculated using the finite displacement and velocity techniques. The influences of the bearing operating parameters on the load carrying capacity, dynamic coefficients, equivalent stiffness, threshold whirl ratio, and threshold rotational speed have been investigated. The results show that special emphasis should be put on determination of the design parameters of the bearing so as to obtain improved steady performance, dynamic characteristics and oil film stability.