In response to the environmental pollution caused by drilling engineering, this study aims 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% 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 proves that the comprehensive performance of the environment-friendly water-based drilling fluid is quantitatively rated as “good”.