The middle- shallow faults, which host a large amount of concentrated oil and gas, are well developed in the Songliao Basin. There exist some differences in development of faults on different reflection interfaces. Previous studies believed they were the products of multi- stage tectonic activities. Based on the modes of faulting in the conditions of previous existing structures, this study analyzed the middle- shallow faulting system using 3D seismic data. The result shows that: (1) the middle- shallow faulting system of the Daqing placanticline in the Songliao basin can be divided into eight types based on faulted successions, displacements, extents and strikes; (2) the average strikes of faults for T2, T1 and T06 reflection interfaces are 322°, 320° and 316°, respectively, with change trend of an anti- clockwise rotation of the faults from bottom up; (3) tectonic stress mechanisms had been transformed from extension during sedimentation of Quantou Formation - Mingshui Formation to strike- slip at the end period of the Mingshui Formation since formation of middle- shallow successions in the Daqing placanticline; and (4) the complicated faulting system in the study area formed from the process of the progressive deformation under the condition of maintaining a relatively steady principal direction of tectonic stress field. The new model for the evolution of the faults reasonably reveals the development rule and mechanism of the middle- shallow faulting system in the Songliao Basin, and will has guiding significance for further exploration and development of the study area.