Abstract: Conventional shear strength improving agents（such as HV-CMC and HEC）can not meet the need of solids-free drilling fluids and environmental protection, due to their potential environmental pollution. Focusing on these issues, the biopolymer was used in this paper as the major material, the novel weakly gelled shear strength improving agent was developed after activating, compounding, and other technology in surfactants. The working mechanism and performance of the novel weakly gelled shear strength improving agent was evaluated. The developed agent was applied in Tarim oil field successfully. Lab research and field application showed that the weakly gelled shear strength improving agent has excellent temperature and salinity tolerances, and it has superior viscosity（above 90000 mpa·s at 0.3 r/min）. At the same time, it is excellent in carry cuttings. It is biodegradable and innocuous, which satisfy with the demand of drilling engineering and environmental protection