The principle and structure of a 10 A high stable DC current source is described. Factors determining the current stability are analyzed and the crucial components including the voltage reference, sample resistor, error amplifier and regulator are elaborately selected to guarantee the current stability. Reasons for oscillation and frequency compensation methods are discussed. The best measurement results show that the relative drift and the relative standard deviation of the current in one hour are about 5.9×10−8 and 9.3×10−8 respectively, and the same characteristics in 10 minutes are about 8.2×10−9 and 4.9×10−8 respectively.