In order to reveal the influence of oil-based drilling fluid on the filtration property of drilling fluid after invading the formation，the effect of organic soil，fluid loss reducer（sulfonated asphalt，oxidized asphalt，2-acrylamide-2-methylpropanesulfonic acid（AMPS），organic amine modified humic acid and their compound）and temperature on the filtration property of drilling fluid was studied by adjusting the oil-water ratio to simulate the drilling fluid intruding formation water. The micro-morphologies of drilling fluids with different oil-water ratio before and after addition of organic soil were observed. The results showed that with decreasing oil-water ratio，the high temperature and high pressure fluid loss of drilling fluid tended to decrease. The organic soil and fluid loss reducer would reduce the high temperature and high pressure fluid loss of drilling fluid. The filtration reduction effect of compound fluid loss reducer was better than that of single fluid loss reducer. Among them，the fluid loss reducer composed by polymer and asphalt had the best fluid loss reduction effect. With increasing temperature，the high temperature and high pressure fluid loss of drilling fluid gradually increased. The micro-morphologies of different oil-water ratio drilling fluids before and after adding organic soil were compared. With decreasing oil-water ratio，the fluid loss reduction effect of organic soil as a suspending agent and tackifier in oil-based drilling fluid system was more obvious. The high temperature and high pressure fluid loss of oil-based drilling fluid could be effectively adjusted by reasonable selection of the types and additions of fluid loss reducer and organic soil.