The water quality analysis of Yangcheng Lake demonstrates higher mineralized degree and hardness of the lake water. The pH value of the lake shows weak alkaline in the eastern part and neutral in the western and central parts. The major ions of the lake water are HCO₃^- and Na⁺ making up 57.4% and 63.9% of the ions. The water type C₁^Na in the western and central pare and C₁^Na in the eastern part. The water mass is contaminated to a certain degree and contains abundant nutrient elements such as nitrogen and phosphorus. The index of ammonia-N and used for assessment of water quality are much higher, as compared to those in the 1970. The non-ionic ammonia index has fallen into weakly polluted IV type water. The nitrite-N index belongs to weakly type IV type water in the western and central parts, except the type I water in the eastern part. The measure to control the pollution development of Yangcheng Lake must be taken effectively, for this lake is an important water source for drinking fishery and irrigation.