Abstract: During the deepwater drilling and exploration operations, since the subsea temperature is relatively low, the subsea hydrostatic fluid column pressure is relatively high, the superficial layer is under-compacted, and the window of pore pressure and fracture pressure of deepwater surface layer is relatively narrow, the well leakage occurs frequently and the equivalent circulating density (ECD) is not easily controlled. In order to solve the above mentioned problems, a new synthetic base drilling fluid with constant rheological property (CR-SBM) has been researched and developed in the foreign countries. Via the investigation and survey on the CR-SBM performance at home and abroad, the rheological stabilizer of drilling fluid has been researched and developed, and the basic formula of constant rheological synthetic base drilling fluid has been established. The rheological property of system in the true low-temperature and high-pressure state is tested by the low-temperature and high-pressure visual device of deepwater drilling. According to the test results, the established synthetic base system has low-temperature constant rheological property.