The rheological properties of liquid phase could directly affect the treatment effect of organic wastewater and municipal sludge in the anaerobic digester. In order to evaluate the flowability of non-Newtonian liquid phase in the reactor, and provide useful suggestions for the choice of the suitable mathematical models (two-phase flow model, multiphase turbulence model, and interphase force model), the gas-liquid two-phase flow of gas mixing in anaerobic digester was studied by numerical simulation. Hydromechanical behaviors, such as velocity field, flow field, dynamic viscosity, etc., of non-Newtonian liquid phase in the anaerobic digester at different flows were discussed. In addition, the effects of multiphase model, interphase force and multiphase turbulence model on the liquid phase velocity were further analyzed. The results showed that an increase in gas flow at the inlet did not significantly affect the flow field form and vortex distribution, but could effectively reduce maximum dynamic viscosity of liquid phase, improve the flowability of the liquid phase in anaerobic digester, especially influence the dynamic viscosity of the liquid phase around the bottom of the anaerobic digester. When the inlet flows were 2.05mL/s and 5.3mL/s, Euler-Euler two fluid model (E-E) and Euler-Euler two fluid model coupled population balance model (E-E-PBM) had very similar simulated liquid velocity to experimental value, and had better simulated velocity than Euler-Lagrange (E-L) model;standard k-ε model, renormalization group k-ε model (RNG k-ε) had better simulated velocity than realizable k-ε model. The simulated velocity matched the experimental value very well when the interphase force was lift force and drag force, respectively.