Constant levels of perceptual quality of streaming video is what ideall users expect. In most cases, however, they receive time-varying levels of quality of video. In this paper, the author proposes a new control method of perceptual quality in variable bit rate video encoding for streaming video. The image quality calculation based on the perception of human visual systems is presented. Quantization properties of DCT coefficients are analyzed to control effectively. Quantization scale factors are ascertained based on the visual mask effect. A Proportional Integral Difference ( PID ) controller is used to control the image quality. Experimental results show that this method improves the perceptual quality uniformity of encoded video.