Exposure accuracy of color digital camera directly affects the performance of color image and the sensory effects of human visual. An automatic exposure method of digital camera based on the color perceiving properties of human visual system, is proposed. A novel kind of exposure estimation function is also established through objective evaluating the sharpness, color saturation and brightness of input images. According to the statistical theory and empirical formulas, the functional relationship between the exposure estimation values and exposure step increment is calibrated and the exposure increment function is established as well. For different brightness properties of current frame, using the exposure increment function, the ideal exposure value of next frame in real time is calculated. A large number of experimental results show that the proposed method for different scenes and different lighting conditions always has a good performance in adjusting exposure value of the captured image. Meanwhile, the algorithm has good robustness which can achieve adjustment for input frames in short time.