Abstract: At present, the drilling fluid coating agents used in domestic oilfield are mainly organic high-molecular compounds. These coating agents show some drawbacks, such as narrow applicability range, poor temperature resistance and salt tolerance performance and worse environmental performance, which can not meet the request of corresponding national standards. Taking the biopolymer as the main synthetic monomer, mixing with nonionic, anion and cationic monomer, an environmentally friendly coating agent coater-10 with temperature resistance and salt tolerance was obtained by aqueous solution polymerization method. The indoor performance evaluation and field application results show that the synthetic coating agent coater-10 can improve the viscosity and shear force of drilling fluid, and reduce the loss of drilling fluid, meanwhile, its temperature resistance and salt tolerance are also better. The contents of main heavy metals, such as chromium and mercury, are within the limited standard level of GB4284-84; the value of acute toxicity test EC50 is greater than 30 000 mg/L, which has little effect on environment; the value of biodegradability BC is 20.1, and this number shows that coater-10 is biodegradable, which is useful for improving the whole environmental performance of drilling fluid system. The ocean drilling fluid system (1#) with environmental coating agent coater-10 meets the demand of drilling engineering and has excellent environmental performance. It reduced the marine environment pollution during the drilling operation.