Abstract: The quantum chaos theory is employed to analyze the statistical characteristics of chaotic EM field in complex cavity. The eigenmode distribution rule for different structure of cavities is investigated by universality of the random matrix theory, then the statistical chaotic characteristics rule of rectangle, sphere and their Boolean combine cavity(Sinna, Stadium) is proposed by the least squares curve fitting method. The results show that regular cavity suchas the rectangle and sphere belongs to low chaotic degree cavity, but their combinations are more chaotic than their linear adding, and Sinna one is more than Stadium one, which means, the concave cavity is more chaotic than that of convex one. The research ideas, the methods and the results could provide theory references for the chaos characteristics research of complex cavity, similarly for the reverberation chamber designing and testing.