This article introduces the drilling process of WFSD-3-P of Wenchuan earthquake fault scientific drilling (WFSD) project. A series of technical measures of high-density and low-filtration drilling fluid system, repeated reaming and mud recharging in pipe trip were taken to overcome drilling difficulties, such as borehole shrinkage in fault gouge formation, rock breaking and collapsed borehole enlarging. As the result, high quality undisturbed cores have been obtained and rich drilling experiences in earthquake fault have been accumulated.