Abstract: Air Quality Index and Composite Pollution Index, as the most commonly used environmental quality assessment methods in China in recent years, took the maximum and average values, respectively of the sub-quality indexes for all the monitoring items. However, the former focused only on the primary pollutant, while the latter ignored the importance differences between pollutants. In order to solve these problems, the coefficient of variation was incorporated to adjust the weight distribution among pollutant items dynamically, and the total quality index was the weighted average of each sub-index. By setting the number of days or months of moving extraction, the sensitivity of the evaluation index to long-term/short-term pollutants was regulated according to the local conditions, which improved the rationality and practicability of these two evaluation methods. The environmental monitoring data of Miyun and Ximaoshan in Beijing from 2015 to 2019 were taken as an instance to verify the effectiveness of these two methods. The spatiotemporal distribution variation of the air quality in Beijing in the past five years was analyzed by the improved method. The results showed that the coefficient of variation of PM_2.5 and PM₁₀ (air quality) together with dissolved oxygen, total phosphorus and total nitrogen (surface water) were larger, and the air quality had been getting better and presented a gradient distribution from north to south.