The invention discloses a constant current source circuit for a direct current load. The constant current source circuit comprises a power supply module, a control circuit, a first drive module, a second drive module, a third drive module and a voltage detection module. The power supply module is connected with the control circuit and the voltage detection module. The control circuit is also connected with the first drive module, the second drive module and the third drive module. The voltage detection module is also connected with the first drive module, the second drive module, the third drive module, the control circuit and the load. The constant current source circuit for the direct current load provided by the invention is applicable to constant current charging of a live direct storage battery. A voltage constant control mode is employed for charging. The storage battery is charged according to 3 phases of constant currents. After the storage battery is charged fully, eddy current charging is carried out on the storage battery again by a small current. The storage battery is not damaged by the small current. Moreover, the electric quantity of the storage battery can be kept at the same time. Through application of the circuit, the charging efficiency can be improved, the electric energy can be saved, and the service life of the storage battery can be prolonged.