In order to reveal the influence of in-situ leaching of rare earth yttrium ore on farmland soil environment,the acute toxic effects of rare earth yttrium and ammonium sulfate (leaching agent) pollution on earthworms were studied by natural soil method. The results showed that the toxicity of only rare earth yttrium or ammonium sulfate was low. The LC50 values of rare earth yttrium and ammonium sulfatein 14 days were 1 216.57 mg /kg and 4 293.53 mg /kg, respectively, for earthworms. When the concentration of ammonium sulfate was higher than 4 400 mg /kg, the toxicity of rare earth yttrium increased significantly and had a synergistic effect. Earthworms at the bottom of the food chain accumulated rare earth yttrium and might cause the gradual enrichment along the food chain.