Abstract: Deepwater drilling raises higher safety and environmental requirements on the drilling fluid. For example, the fluid must have strong inhibition performance and excellent lubricity. It should not produce gas hydrates easily and should have such characteristics as simple maintenance, easy operation, and improved drilling speed. To prevent clay swelling, polyamine inhibitors, low-molecular coating agent, anti-balling lubricant, and flow regulator are used to build a deepwater HEM polyamine fluid system with strong inhibition performance, and the hydrate software simulation is used to calculate the formula of inhibiting hydrate formation. HEM polyamine fluid has been successfully applied in 15 wells in the South China Sea and lays the foundation for the prevention of gas hydrate formation in deepwater drilling process.