The invention discloses a beneficiation reagent adding device and method. The beneficiation reagent adding device comprises a reagent adding machine, a reagent storage box and a low-voltage numerical-control device. The reagent adding machine is arranged in the reagent storage box. The electrical appliance part of the reagent adding machine is connected with the low-voltage numerical-control device, and a flow-limiting valve is installed on a reagent feeding pipe of the reagent adding machine. A reagent is pushed through the reagent adding machine to enter the reagent feeding pipe from the reagent storage box and then added into flotation work or tailing thickening system, and the basic flow of the reagent is set according to requirements; adding of the reagent according to the basic flow is achieved through the flow-limiting valve; the power of the reagent adding machine is regulated through the low-voltage numerical-control device, so that conventional adjustment of the reagent flow is achieved. The problems that in the reagent adding process, agglomeration and flow interruption are caused, the valve is blocked, and components are instable are solved. The automation degree of a reagent adding system is improved.