Abstract: Since there is no specialized environmental standard for drilling fluid in China, the direction of optimizing the environmental protection in drilling fluid system is ambiguous. In this paper, we investigated the COD, BOD, biological toxicity, heavy metals (Hg, Cd, Cr, As, Pb) and the content of benzopyrene and other environmental control indicators of both water-based drilling fluid and treating agents in northwest oilfields for testing and evaluation. According to the two standards of "National Integrated Wastewater Discharge Standard"(GB 8978-1996) and "Soil Environmental Quality Standard for Farmland", the evaluation results showed that the BOD and COD contents of water-based drilling fluid in Northwest Oilfield were between 30-3000 mg/L, and benzopyrene content was more than 0.0003 mg/L, far exceeding the three criteria of GB 8978-1996. Besides, the compliance rate of the these three indicators for the drilling fluid treatment was nearly 100%; heavy metals (Hg, Cd, Cr, As, Pb) partly achieved Level 3 in the criteria of GB 8978-1996, of which cadmium, chromium and lead are the major concerns. It recommended that in the actual control of indicators for the drilling fluid system, appropriate emission standards should be set respectively and the drilling fluid system and treatment agents, especially for lubricants, fluid loss and other indicators of environmental protection testing should be strengthened, laying the technical foundation for developing the environmentally-friendly drilling fluid system and testing standards in the future.