The invention discloses a stream quantitative feeding device for a nucleating agent. The stream quantitative feeding device for the nucleating agent comprises a nucleating agent container, a discharging runner and a baffle, wherein a containing cavity is formed in the nucleating agent container, the nucleating agent is contained in the containing cavity, and a discharging hole is formed in the lower end face of the nucleating agent container; the upper end of the discharging runner is arranged at the lower end of the discharging hole in a rotating mode, and the lower end of the discharging runner extends downwards in a tilting mode; one end of the baffle is movably arranged at the discharging hole, and a connection rod extends downwards from the other end of the baffle and is connected with the discharging runner; and a spring used for providing reset force for the baffle is arranged between the upper surface of the baffle and the lower end face of the nucleating agent container. By means of the stream quantitative feeding device for the nucleating agent, the technical problems that a nucleating agent is poor in nucleating effect and prone to fading and is used too much are effectively solved, and the quality of castings is effectively improved.