In the industrial process of producing the strong phosphoric acid (SPA), clarification of the solution is essential to the ultimate product. However, the large viscosity of sediment and the induced interface interaction result in difficulties when the SPA is clarified. CFD numerical methodology is applied to simulate internal flow field and performance of the low speed scraper based on Mixture solid-liquid two-phase flow model. Sediment deposition is generated by loading solid particles at the bottom of clarifying vessel. The moving mesh and RNG model are used to simulate the rotational turbulent flow in clarifying tank. Variables studied, amongst others, are the scraper rotation speed and the mounting height, which can affect the solid suspension height. Features of flow field and solid volume fraction distribution in computational domain are presented and analyzed. The numerical reports of the scraper torque and velocities of inlet and outlet filed are obtained. It seems the torque value of rotational axis and particle suspending height augment with an increasing rotating speed. Meanwhile, a high revolving speed is good for the deposition discharge. The particle fraction distribution in meridional surface and horizontal surface at fixed rotation speed are analyzed to determine the corresponding optimal installation height. The simulating results reflect the flow field is marginally stirred by the scraper and proper working parameters are obtained, in which case the comprehensive properties of the scraper and the clarifying tank are superior.