The hematological studies on common carp (Cyprinus carpio) in three different environment - net cage, pond and reservoir were carried out by surveying and comparing the red blood cell count (RBC ), the white blood cell count (WBC ), the hemoglobin content (Hb), the color index (CI), the hematocrit value (HV) and the blood sedimentation rate (BSR) of 115 specimens. The results of the test are summarized as follows: (1) Significant differences of RBC and Hb between the fingerling in net cage and in pond were found. The RBC, Hb and HV of adult carps in net cage are significantly higher than those in pond, but the WBC and CI have no significant difference between them. (2)The RBC and HV of adult carps in net cage are significantly higher than those in reservoir,but the CI and BSR of adult carps in net cage are significantly lower than those in reservoir,the WBC and Hb have no significant difference bctween them.