根据１９９６年对密云水库调查的部分结果，分析了该水库生物理化环境的现状和变化趋势，并进行了营养程度评价。结果表明：水温有明显的４季变化，溶解氧和ｐＨ适中；无机氮含量丰富，无机磷很缺乏，Ｎ／Ｐ大大超过１６／１，浮游植物数量和生物量年平均值分别为４０５５５×１０５Ｌ－１和３０１３５ｍｇ／Ｌ，浮游动物数量和生物量年平均值分别为６５２６６１Ｌ－１和２４７１２ｍｇ／Ｌ。与历史同期相比，无机氮略有下降，无机磷下降很显著，但浮游植物量却有很大提高。密云水库为中营养型水库，但有富营养化趋势。 Based on the partial results of the survey on Miyun Reservoir in 1996, the status and trends of the biophysical and physical environment of the reservoir were analyzed and the nutritional level was evaluated. The results showed that water temperature had obvious seasonal change, dissolved oxygen and pH were moderate, inorganic nitrogen was abundant, inorganic phosphorus was scarce, N / P was over 16/1, phytoplankton biomass and annual average was 40555 × 105L-1 and 30135mg / L, respectively. The average numbers of zooplankton and biomass were 652661L-1 and 24712mg / L, respectively. Compared with the same period of history, the inorganic nitrogen decreased slightly, inorganic phosphorus decreased significantly, but the amount of phytoplankton has greatly increased. Miyun Reservoir is a medium-nutrient reservoir, but has the tendency of eutrophication.