Due to the limitation of dynamic range, it needs to control the exposure time and automatic gain for traditional cameras to obtain clear information of the target scene through reducing the influences of pixel saturation and overflow. In order to obtain a clear image simultaneously including dark and bright field information, the dynamic range of the CMOS image sensor must be extended. In this paper, a dynamic range expanding method of CMOS cameras based on binary image superposition is proposed. By superposing a series of binary images with a logarithmic exposure time, the image detection dynamic range of the CMOS camera is improved. As a result, the camera can simultaneously detect strong and weak signals even in the environment with a large brightness variation, and obtain clear gray images of the target scenes. The experimental results show that the relative dynamic range of this binary superposition CMOS camera can be enlarged to more than 8 times that of the traditional counterpart. A comparison of image brightness curves shows that this camera has an effective logarithmic response output. This camera can also effectively reduce the saturation overflow in the bright part and the loss of details in the dark part of the image, and can obtain a complete clear and uniform image in both the highlighted and backlit parts.