The invention discloses a niclosamide controlled-release dispersing agent for killing schistosoma japonicum cercaria and a preparation method thereof. The niclosamide controlled-release dispersing agent for killing the schistosoma japonicum cercaria is characterized in that the compositions of the niclosamide controlled-release dispersing agent are niclosamide, paradichlorobenzene, floating carriers and a dispersing agent and the main compositions of the niclosamide controlled-release dispersing agent are the niclosamide and the paradichlorobenzene, wherein the weight ratio of the niclosamide to the paradichlorobenzene is between 10 and 30 to between 90 and 70. The niclosamide controlled-release dispersing agent and the preparation method have scientific and reasonable formula and ratio, advanced and simple technique and good effect of killing the schistosoma japonicum cercaria. The controlled-release dispersing agent for killing the schistosoma japonicum cercaria, which is prepared by processing the niclosamide, the paradichlorobenzene, corncob particles and so on as materials, is applied to a pathogen generation water area, releases the niclosamide at a fixed quantity in virtue of sublimation of the paradichlorobenzene, freely diffuses in virtue of the molecular tension and the function of the dispersing agent, reaches the predicted concentration in a water body, has long lasting period, effectively kills the schistosoma japonicum cercaria, and prevents the schistosoma japonicum cercaria from infecting human beings and livestock; and the death rate of the schistosoma japonicum cercaria reaches 100 percent.