In order to detect the low contrast targets in the complicated background, the time division full polarization imaging system based on dual liquid crystal variable retarders (LCVR) is developed, and an optimum combination scheme based on the minimum 2-norm is proposed in the control of LCVR phase retardation. The system instrument matrix is calibrated with the optimum phase retardation combination, and the field imaging experiment is carried out when the green coating targets are hidden in the shade. The experimental result shows that the contrast between the target and its background is almost zero in the ordinary intensity image and 0.2525 in the S0 image obtained by inversion. The achieved result further proves that the system can effectively realize low-contrast target detection in complex background.