Abstract: Various complicated situationsoccur in shale gas well drilling with the conventional polymer drilling fluid.In order to select suitable drilling fluid system for shale gas well drilling,complex situations and shale cores were analyzed and researched seriously in drilling shale formation.Through the technical investigation,cationic emulsion polymer drilling fluid was selected.Laboratory evaluation of this drilling fluid was carried out through a series of experiments including routine performance,inhibition performance,cuttings pollution resistance,lubricating performance and reservoir protection evaluation,and the cationic emulsion polymer drilling fluid was applied in the Well Xiangye 1 and Well Pengye 1.There were no tight hole and stuck pipe events in the course of drilling the two wells,the average rate of hole diameter enlargement was less than 8%,the inhibitive performance,reservoir protection and lubrication all meet the requirements of shale drilling operation.The research shows that,the cationic emulsion polymer drilling fluid has solved the problem of shale wellbore stability and reservoir damage effectively,drilling cycle and drilling fluid cost were reduced,good economic benefits were achieved,valuable reference experience was offered for the shale gas exploration and development.It was predicted that the cationic emulsion polymer drilling fluid system has a good prospect of application and promotion for drilling shale gas well in the future.