Abstract: In order to apply KCl polymer drilling fluid system to low porosity-low permeability reservoirs better,its anti-water lock performance was studied. Based on the research of water locking damage mechanism and anti-water lock technical countermeasures,such as adding anti-water lock agent FCS and oil-film temporary plugging agent GPJ to optimize KCl polymer drilling fluid system,were put forward,and their anti-water lock effects were evaluated. Core spontaneous imbibition test showed drilling fluid filtrate saturation decreased from 76.24% to 35.41%,suggesting great improvement in the anti-water lock performance of the drilling fluid. At the same time,the depth and amount of drilling fluid filtrate reduced significantly;flowback capacity increased greatly;the permeability recovery rate tested by the core dynamic pollution reached over 90% after the optimization of the drilling fluid. The method to improve the anti-water lock performance of drilling fluid was practical,which extended the application scope of KCl polymer drilling fluid system to low porosity-low permeability reservoirs.