The parasite Rhadinorhynchus chongmingnensis infects the digestive tract of the carp, the intestines wall tissue is damaged immediately, a lot of epithelial cells proliferated from the intact tissues to cover damaged positions. At same time, the damaged tissues grow granulation tissue and form granuloma, and the adherence of internal organs occurred. Other organs of the diseased fish such as liver, pancreas and kidney are also damaged to varying degrees. The process of forming, developing and disappearing concerned with granuloma is observed and described.The contents of K, Na, Cl, CRE and BUN in serum of diseased fish are almost the same as the healthy fish. Only GOTs and no GOTm exists in the serum whether the diseased or the healthy fish, the total GOT actively in serum of diseased fish is distinctly higher than that of the healthy ones. The neutrophil content showed by percentage in leucocyte quantities of diseased fish is higher than that of healthy fish.The middle host of Rhadinorhynchus chongmingensis is Moina dubis. Using quick lime (CaO) or beaching powder (CaOCl₂) to sanitize fish pond before stocking is efficacious in prevention.