Abstract: There are a number of large low porosity and low permeability oil and gas fields in the Xihu sag of the East China Sea. Most of these oil and gas fields are deeply buried, with poor lithology homogeneity, loose cementation of sand and mudstone interlayer and coal seams developed in the center, which are easy to lead to complicated conditions during drilling such as the hydration expansion of mudstone, peeling blocks and coal seam collapse. PEM drilling fluid system is widely applied in the Xihu sag of the East China Sea, with good application effect and economy. In order to meet the requirements of high temperature deep wells with increasing depth in the East China Sea, reduce drilling complicated conditions, and better protect low porosity and low permeability oil and gas reservoirs, through experimental research, the high temperature stability, inhibition, plugging loss reduction and bentonite addition of PEM system are optimized and evaluated. The optimized PEM system has a temperature resistance of 180 ℃, good rheological properties and low water loss, the rolling recovery rate of 92.5% at 150 ℃, and the lubrication coefficient of 0.087～0.11, which has achieved good results in application. Using logging data, the depth of drilling fluid invading into the reservoir is less than 30 cm, and the reservoir protection effect is good. The drilling fluid system has achieved good application results in many oil and gas fields with poor porosity and permeability conditions and complicated geological conditions in the Xihu sag of the East China Sea.