To study the classification, compositon and the role of different types of hemocytes in immune response in Eriochior sinensis, we researched the composition and classification of hemocytes from E. sinensis using cytochemical assays, cytoenzymatic assays and morphological observation in this investigation. Meanwhile, total hemocyte counts (THC) and different hemocyte counts (DHC) were performed. Our results showed that hemocytes from E. sinensis were divided into four types: granulocytes (G), intermediate granulocytes (IG), semigranulocyte (SG) and hyalinocytes (H). SG got the highest percentage about 33.54% while IG got the lowest only about 15.31%. Only granulocytes showed positivity to acid phosphatase, alkaline phospatase, β-glucuronidase and phenoloxidase and all types of hemocytes contain polysaccharide but no lipid. In addition, the THC increased obviously at 3 h after the injection of Aeromonas hydrophilia and reached a peak at 6 h, which was significantly higher than blank and saline groups. The numbers of granulocytes declined dramatically and hyalinocytes increased at the same time during the infection of bacteria, and this phenomenon recovered to their normal level 6 h later. Therefore, we concluded that hyalinocytes perform phagocytosis with large numbers of proliferation while granulocytes perform release of the immune-related enzymes with cell lysis during the response in non-specific immunity in E. sinensis. In addition, there might be transformations between various types of hemocytes and intermediate granulocytes were the interim types during the transformation. Hemocyte classification in crustacean had been studied by several researchers but there was no final conclusion in this field. The method of three categories was adopted by most researchers. However, the author found that there was one intermidiate type of hemocytes and it would be helpful to the research of hemocytopoiesis and immune function of different types of hemocytes.