In response to the environmental pollution caused by drilling engineering, to develop an environment-friendly water-based drilling fluid system. Guar gum ( GHV-90) , pregelatinized starch ( GK-K325) , and modified castor oil ( PCMAS5) were selected as additives. Adopting orthogonal experimental design method, the optimal formulation of the drilling fluid was: 1% sodium based bentonite( Na-B) + 0. 6% GHV-90 + 1. 5% GK-K325 + 1% PCMAS5. A comparison was made between this environment-friendly drilling fluid and special formation drilling fluids, conducting linear expansion tests, rolling recovery tests, core permeability compression tests, anti-pollution experiments, and biotoxicity tests. Finally, expert opinions were introduced to establish a fuzzy evaluation model. The results show that the comprehensive performance of the environment-friendly water-based drilling fluid is quantitatively rated as good.