Abstract: Based on a series of numerical calculations, the behavior of flow field in obstructed square buoyant vertical jet is summarized and analyzed. Based on the axial line velocity distribution, the flow after the disc can be divided into three regions: i.e. recirculation region, transitional region and selfsimilar region. The characteristic of self-similarity of upright velocity was validated. The three regions can also be distinguished based on the axial velocity. The axial velocity in self-similar region was found to obey the same law and the formula was presented by introducing the velocity expression used by Chen and Rodi. The isolines of pressure on cross sections of different heights were displayed and the production, expansion, breaking and disappearing of negative pressure regions were found.