Abstract: In this paper, the activities of the equatorial anticyclones, which occured during the period from July to September in the years 1979-1983 in the region (10°S-15°N, 90-140°E), were investigated. Among them, 15 anticyclones of similar strength and similar size were selected and used to do the composite analysis, the characteristics of their three-dimensional structure were obtained. The results show that the epuatorial anticyclone is a warm mid-lower layer system. Its anticyclonic circulation cooperates well with the vorticity, divergence and the vertical motion. In the lower layers of theequatorial anticyclone, there exist negative vorticity, divergence and subsidence in thecirculation center. But surrounding it are positive vorticity, convergence and ascendence.In the upper layers just opposite conditions can be seen. Heating field has good relation with the vertical movement. In the center is the diabatic heating induced by subsidence.The calculation of the vorticity budget shows that there is negative vorticity assemblage in the mid-lower layer and positive vorticity assemblage in the upper layer, and the local variation of vorticity is mainly due to the divergence term, the advection term and the vertical transport term.