In order to put forward the impeller cutting law of double channel pump, two kinds of double channel pumps with the specific speed of 77 and 122 were selected as research objects. The impeller was cut as five times respectively and the performance experiments of double channel pumps were conducted. By investigating the change law between the performance parameters and the impeller diameter at optimal point and dead point, the corresponding value range and equation of cutting index were obtained. Results show that the flow rate, head, shaft power and efficiency reduce with the decrease of the impeller diameter. However, as the increase of impeller cutting percentage, the change law and the reducing amplitude of performance parameters at optimal point are different, and head and shaft power obviously decrease with the decreasing of the impeller diameter at dead point. The cutting index number of double channel pump at dead point can be viewed independent of the specific speed while the change of the cutting index number is obvious with the change of the specific speed at the optimum and common points. The predicted value of the cutting law according to the impeller cutting law established agrees with the experimental value well.