This paper introduces the principle and actual operating environment of the direct current optical-electronic current transformer that is the first one in China. The field calibration method of the direct current optical-electronic current transformer is proposed. According to the actual operating， error analysis of the results is given and some suggestions are proposed. The practical operation results of the direct current optical-electronic current transformer show that its accuracy satisfies the design requirement and the laser power supply can adapt the field operating， and the calibration standards and equipment for the direct current optical-electronic current transformer at the scene need to be established.