Abstract: During drilling shale gas wells in the Fuling Area, the oil-based drilling fluid is often lost seriously due to bedding and developed fractures. To address this problem, a nano-micron deformable spherical gel was developed after the geological characteristics of shale gas and properties of oil based drilling fluid were analyzed, and sheet or fibrous plugging materials were selected additionally to form the composite microsphere gel plugging agent on the basis of compatibility and sealing performance evaluation. Laboratory evaluation showed that the thickness of mud cake at high temperature and high pressure (HTHP) decreased from 4.0 mm to 1.5 mm, permeability reduced by 97.66%, and the pressure-bearing capacity of quartz sand bed (20 to 40 mesh) increased from 2 MPa to 17 MPa after adding microsphere gel plugging agent by 2.4% into oil based drilling fluids. This agent was applied to 66 wells in Fuling Area, and the results indicated that composite microsphere gel plugging agent was well compatible with oil-based drilling fluids, and it can prevent or reduce the loss of drilling fluid by plugging micropores and microfractures in drilling operation, so as to decrease the loss of oil based drilling fluids effectively.