Abstract: The Wei Ⅱ and Liu Ⅱ section of WX exploration area in South China Sea are easy to collapse, the well wall is prone to instability and collapse. In order to ensure the safe,efficient drilling and the high-yield development in this region. The drilling fluid system must simultaneously solve the reservoir protection and the collapse of wellbore wall. In this paper, firstly, the drilling fluid system used in the area was analyzed and summarized, and then the theoretical analysis and experimental research on the anti-sloughing inhibition of formate and polymer alcohol and the synergistic effect between the two were carried out. The research shows that: formate polymer polyol drilling fluid system has good anti-sloughing inhibition, lubrication and drag reduction effects, and the solid content is low, which is conducive to reservoir protection. Despite the high prices, it can be recycled and used, and the drilling comprehensive benefit is excellent. It is recommended to use the formate polymer polyol drilling fluid system in the reservoir interval of WZ oilfield.