Abstract: One of the most characteristic atmospheric circulation processes is that summer subtropical high over Pacific moves northward and extends westward, which affects China’s weather and climate significantly. Subtropical high over Pacific moves northward by the effect of meridian heating field changing from June to August each year. It is the seasonal catastrophe of the Northern Hemisphere to global atmospheric circulation, especially by jumping northward. Mechanism of summer subtropical high moving northward was discussed by applying dynamical system theory and method. Baroclinic atmospheric system containing ultra-long wave, long wave and zonal current interacted was built firstly, then phase trajectory figure, stream function figure, Poincaré section map and phase variable time graph were used to analyze the evolving of system states and circulation patterns, especially to examine subtropical high and its moving northward seasonally, by the effect of summer zonal inhomogeneous inposed thermal field together with friction dissipation. The nonlinear system theory and method were used to discuss subtropical high var iation mechanism and new research were explored:(1)the higher steps dynamical system(22 variance) considering ultra-long wave,long wave and zonal flow which interacted was built.(2)it was designed to a summer inhomogeneous thermal field of two-ocean and two-continent in the Northern Hemisphere.(3)The system states were analyzed synthetically by phase trajectory figure,Poincaré section map and phase variable time graph, and the states distribution of parameter plane ( θ ，k) was drawn, and stream function isoclines graph of rectangle pas sage(to be shown as the Northern Hemisphere approximately) was also drawn by re newed stream function.Several characteristic circulation patterns were sum up,a nd the distribution of circulation patterns were acquired with the plane(θ ，k).Subtropical high moving northward was discussed by combining system states and circulation patterns.The main results were as follows: (1) There were seven regimes of flow,and states came through H→R1→R12→V-NV→C along with value k minish,and through R1→R 12→V-NV→R 2 along with valueθ increase.(2) There were four circulation pa tterns,and patterns came through W→G1→G2 →G3 along with value k minish,and through G2 →G3 along with value θ increase.(3) It was rep resented that circulation pattern came through G2 to G3 for summer subtropic al high moving northward and extending westward,and it was that regimes of flow transformed Rossby regimes into vacillation states (R12→V-NV) correspon ding to that change.Transmeridional and south-north vacillation movement where subtropical high was leaning to north was corresponding with maintaining vacill ation states. The system,which was established in this paper,was capable of depicting the regimes of flow and circulation patterns of special season.It revealed the possible mechanism of subtropical high moving northward seasonally and vacillation in c ertain season,which was forced,dissipative and nonlinear atmospheric system tran sferred from waves to vacillation and to be kept.There are several questions to be discussed as follows:(1) The results above bel ong to the category of dynamic systemic qualitative analysis and numerical exper iment, and it makes the system closed to the actual instance because of consider ing the effect of long wave and zonal heterogeneous field. It helps to understan d the mechanism of subtropical high deeply. (2) Rectangle passage flow was used to replace flow regimes of annulus passage approximatively, then to replace the Northern Hemisphere circulation. These problems should be improved more.