Formations were extremely complicated in WFSD-4 of Wenchuan earthquake fault scientific drilling project, and the drilling construction was also very difficult. Higher drilling fluid technology was required. The potassium lime polysulfonated drilling fluid system was selected as the WFSD-4’s main system. The paper introduced the use and maintenance of drilling fluid systems used in each borehole section. In addition, the special process of drilling fluid technology and the response to complex situations are introduced in detail.