Abstract: Natural gas hydrate can be easily formed from the water base drilling fluid during the deep water drilling, which will affect the normal progress of drilling operation. To solve the problem, a reaction equipment was designed and developed, which can simulate the temperature and pressure conditions of deep water drilling .The effects of additives used in water drilling fluids including CPAM, 80A51, HPAM, FA367, NW-1, MP-Ⅱ, HEC, MC, XY-27, SMT, FCLS, EG600, HCOONa, HCOOK and NaCl on natural gas hydrate formation were investigated. And the subcooling degree of drilling fluid system was obtained. The result shows that CPAM, 80A51,HPAM, FA367, NW-1, SMP-Ⅱ, HEC, CMC, XY-27, EG600, HCOONa, HCOOK, NaCl and KCl can inhibit the formation of natural gas hydrate to some degree, but SMT and FCLS can help the formation of natural gas hydrate faintly in water base drilling fluids. The inhibition of the ion species of polymer additives on gas hydrate can be ignored.