Abstract: In recent years, a large number of low permeability resources have been found in the deep reservoirs of East China Sea, which are mainly developed by horizontal wells. This type of reservoir has deep burial depth, high temperature, complex pore throat characteristics, and is easily damaged by water lock, which poses a challenge to the temperature resistance and reservoir protection performance of horizontal section drilling fluid. By selecting NaCOOH weighting agent and optimizing SATRO waterproof locking agent dosage, the temperature resistance of drilling fluid system was improved and the risk of water lock was reduced. The experimental evaluation results showed that all performance indicators met the requirements. The optimized solid-free drilling fluid was applied in 4 wells, and the initial production capacity reached the production allocation. Compared with the adjacent wells, the production capacity was significantly improved, and the reservoir protection effect was good. It has good application value.