The quality of construction of cutoff wall plays a vital role to its upper structure and normal operation of dam. In order to study the construction defects of concrete cutoff wall to the effects of dam seepage flow field and investigate the effects of seepage face freezing in winter on the dam. Combining a water conservancy project in north, the control section and super finite element mesh automatic generation method was used to set up the 3D finite element model and conduct the steady seepage analysis. Analysis results show that the groundwater level has landed in the cutoff wall simultaneously reduced the exit gradient downstream slope seepage and improved the stability of the slope. The effect on construction defects of cutoff wall in seepage field is more obvious in the local range. Winter freezing on dam seepage face has little effect.