A new model for estimation of just-suspension speed in a stirred tank is proposed based on the forces acting on a single stationary particle on a flat plate in the presence of a simple shear flow. We suggested that if the lift force acting on the particle is greater than the difference between gravitational force and buoyancy force, particle lifts off. However, if the lift force is smaller than the difference of these two forces, particle settles. In order to estimate the lift force component acting on the particle, a simple 3-dimensional of CFD model is generated. By simulated lift force component, the representative flow velocity subjected to the radius of the solid particle for just-suspension is determined. For estimation of the representative flow velocity, flow velocity distributions inside stirred tank is employed at the inlet of the CFD model as a customized boundary condition. The boundary condition is determined based on direct measurement of flow velocity close to the tank base using L.D.V. It is showed also that flow visualization close to the tank bottom using P.T.V. agrees well with the L.D.V. results. The representative flow velocity obtained from the CFD model is verified and compared with the experimental value at just-suspension speed for a wide range of particle densities, 0.03 <=Delta rho/rho(1)<= 1.5. The results showed that the calculated value agrees reasonably well with the experimental value within the error of +/- 15% at a given system using a 4 bladed pitched paddle impeller. The determination of the effect of lift force acting on a solid particle for solid-liquid suspension in a stirred tank may overcome the limitation of the conventional experimental method by visual observation for characterizing the just-suspension speed. Moreover, the new proposed model also offers physical understanding in regards to explaining the mechanism of just-suspension which has not been reported by earlier workers.