Considering serious water pollution problems in Liaohe River, this paper studies the water quality of Liaohe River's trunk stream from 2008 to 2017 by fuzzy comprehensive evaluation and weighted average of membership degree methods. The results showed that based on factor analysis of main evaluation indicators through dissolved oxygen, chemical oxygen demand and ammonia nitrogen, the maximum weight of dissolved oxygen of Zhuershan State control monitoring section in Tieling was 72%; the maximum weight of dissolved oxygen index of Xingan State control monitoring section in Panjin was 57%. The average dissolved oxygen index of the two sections were 7.13 mg/L and 6.66 mg/L, respectively. In addition, the temporal and spatial distributions of the river's water quality were obtained from the study. The variation of water quality in Zhuershan section flacutated between 2.23 and 1.34 after 2011, whereas the variation of water quality in Xingan Section shifted between 2.26 and1.36 after 2013. Water quality of Zhuershan section improved obviously and was much better than Xingan Section, which meant remarkable achievements had been made in water pollution control. Therefore, the results of the study are of great significance to control water pollution for Liaohe trunk stream.