Abstract: Based on monthly mean data including NCEP/NCAR reanalysis, CMAP precipitation, GODAS oceanic current, and SODA wind stress from 1981 to 2015, we have investigated the characteristics of seasonal changes in the South Pacific Convergence Zone (SPCZ) and possible mechanisms for the SPCZ formation and maintenance. A key region of the SPCZ is identified. The results show that in the SPCZ region, there is a transition from convergence zone caused by wind shears between easterly and westerly winds to that caused by easterly winds in April, and an opposite trend of transition occurs in December. In the middle and lower troposphere, the upward extension of the SPCZ and convergence are significantly higher and stronger in winter than in other seasons. Two mechanisms explain the formation and maintenance of the SPCZ. First, topography plays a certain role. When blocked by topography, the equatorial vortex travels along the Australian terrain. Such condition is conducive to the formation and maintenance of the anticyclonic circulation in the Australian region and the cyclonic circulation in the SPCZ region. Meanwhile, with the effect of the Coriolis force, warm sea water tends to converge in the SPCZ and forms an area with high SST, which heats the atmosphere above and contributes to the formation and maintenance of SPCZ. Second, diabatic heating imposes essential impact on the SPCZ. Heat source in the SPCZ warms the atmosphere above and produces the zonal gradient forcing, which drives convergence in the lower atmosphere. All results are meaningful for scientists to better understand the global circulation, especially that in the southern hemisphere.