Usually， the Region of Interest(ROI) video coding algorithm is implemented by using a smaller quantization parameter(QP) or more bit-plane inside ROI. It caused the degradation of quality by the artifacts of boundary and additional bit-rate burden in ROI. This paper proposes the grid quantization algorithm to avoid these disadvantages. The macroblocks inside of ROI are divided into three kinds: Grid A， Grid B and Gradient. Different partition has different quantization parameter based on visual masking effect. The test results show that the proposed algorithm can promote the ROI objective quality about 1.9dB on average， and the subjective quality is also improved obviously. Compared to other ROI quantization algorithm， the ROI quality is improved by 0.47dB， while the whole picture quality is improved by 0.625dB. The proposed algorithm can reduce the bit-rate burden of ROI and maintain subjective quality.