Based on analyzing the noise properties of CCD camera, a new method was proposed for testing its electronic gain. Applying arbitrary scene, the linear relationship between the image signal SDN and the image noise σDN was deduced with an improved algorithm, and the electronic gain of the CCD camera was calculated. Different from the traditional methods which apply integrating sphere or uniform light source required by EMVA 1288 standard, the new method presents the characteristics of simple operation and high economy. Comparison experiments were performed between the traditional and the proposed methods, and the results indicate that, the new method can test the electronic gain of CCD cameras precisely and effectively with a high repeatability.