The utility model discloses a prevent device of rare phosphoric acid depositing reservoir scale deposit, the bottom of depositing reservoir body is provided with the discharge opening, the discharge opening links to each other with the magma circulating pump, the center of depositing reservoir body is provided with the draft tube, the lower extreme nozzle of draft tube is tubaeform, the lower part of depositing reservoir body is stretched to the draft tube, from the top down distributes and has multirow circulation hole on the section of thick bamboo wall of draft tube, the upper end center of depositing reservoir body is provided with Y shape blender, phosphoric acid pipe and magma pipe are continuous with two imports of Y shape blender upper end respectively, the lower part that the draft tube is stretched to Y shape blender, the export of magma circulating pump is connected to magma outer discharge pipe and magma pipe respectively. Need not mechanical stirring, eliminate local supersaturation in the depositing reservoir through extrinsic cycle in the magma, promote crystal growth, obtain that the crystallization thickly, easy is filtered, few sludge is carried secretly to phosphoric acid, effectively suppress depositing reservoir inner wall scaling, promote depositing reservoir cycle of operation, reduce the clearance degree of difficulty and cost.