In this experiment, the blood of 185 healthy fish including grass carp, black carp, wuchang fish, silver carp and bighead carp were measured, 1367 data including erythrocyte, hemoglobin, blood sugar, total protein, albumin, urea nitrogen, cholestrol and triglyceride were obtained. Through the reliable analysis, the average error rate of all the data was less than that of the biological tests in investigutions except that the blood sugar has a relative error above 5%. The results of experiments have shown as follows:1. The blood indexes of fish are variable with species Except for the erythrocyte, the value of other seven indexes is in the following order: carnivorous fish herbivorous and omnivorous fishesfiltering feeders.2. The blood indexes of fish are affected by the environmental conditions The values of blood sugar, total protein, albumin, hemoglobin and urea nitrogen of wuchang fish and grass carp reared in running water are much higher than those of the pond fish.3. The blood indexes also related to the nutrtive availability. Fish of higher nutritive value can be cultured by taking natural organisms as the main food source and the commercial food as supplementary.