Putaohua oil layer of Daqingzi well area in southern Songliao Basin is sandstone reservoirs with low-medium porosity，low permeability and thin layer. The characteristics，spreading regularity and quality controlling factor of the peripheral sand body reservoirs are unclear. The reservoir characteristics have become a restrictive factor of the exploration and development. The reservoir characteristics were researched based on cores，casting thin sections and conventional mercury injection and other analytical data. The result shows that the sand body in the braided channel crotch will be the favorable reservoirs with rock type of debris arkose and pore type of secondary dissolution pore and residual primary pore. It has welldeveloped pore structure as medium-porosity and medium-throat type. Daily production by oil test is high. Sedimentation is the basic factor and dissolution among diagenesis is the key factor for the formation of favorable reservoirs in the braided channel crotch.