The feasibility of polymer flooding in high-temperature and high-salinity reservoir by using diutan gum was explored. Xanthan gum and konjac gum were used as comparison to investigate the rheological property, the capability of mobility control and EOR (enhanced oil recovery). The results of steady-state rheological property and mobility control show that the order of the capability of thickening and mobility control in porous media are as follows: diutan gum > xanthan gum > konjac gum. Compared with the other two biopolysaccharides, diutan gum has better temperature- and salinity-tolerance characteristics and good long-term stability in high-temperature environment. Based on the wettability modification of quartz sand surface (modified into oil wet) and the changes of hydrodynamics radius of the injected and produced fluids, the main mechanism of establishing resistance of three biopolysaccharides was analyzed. For konjac gum, xanthan gum and diutan gum, the contribution rate of mechanical trapping to the dynamic retention of porous media was 45.90%, 60.78% and 81.83%, respectively. The larger hydrodynamics radius of the diutan gum makes it easier to be trapped by porous media, and the ability to reduce the water phase permeability in porous media is stronger. Additionally, in the laboratory oil displacement experiment, the EOR of diutan gum is up to 24.31% OOIP (original oil in place), which is significantly higher than xanthan gum (17.02% OOIP) and konjac gum (8.19% OOIP). It is expected to be a promising oil displacement agent for enhanced heavy oil recovery in high-temperature and high-salinity reservoirs.