With the promulgation of environmental protection regulations and the enhancement of environmental protection concept, the requirements for environmental protection performance of oil field drilling fluid system are becoming more and more stringent. Therefore, an environmentally friendly and strongly inhibited water-based drilling fluid system suitable for shale gas horizontal wells has been formed with HBYZ-2 and CQHY-3 as main treatment agents and other additives, and its comprehensive performance has been evaluated indoors. The results show that the rheological properties of the drilling fluid system are stable and thermal stability is good after aging at 150℃. The system also has good plugging property, inhibition, lubrication, anti-pollution and reservoir protection properties. The biotoxicity EC50 value of the drilling fluid system is more than 30 000 mg /L, BOD5 /COD value is more than 25, which meet the standards of non-toxicity and easy degradation. The content of main heavy metals is also far below the standard value, which has good environmental protection performance. The field application results of environmentally friendly and strongly inhibited water-based drilling fluid system in Well CX-1 and Well CX-2 show that there are no complex situations such as borehole wall instability and collapse, low pump pressure, low friction, smooth tripping, and stable drilling fluid performance in the two wells during drilling, which indicates that environmentally friendly and strongly inhibited water-based drilling fluid system can meet requirements for shale gas horizontal well drilling.