Aiming at the problems of grey deviation and weak anti-interference ability of the traditional GM(1, 1)model, a grey Markov model with equal dimension and new information was established. The model adopted grey Markov model to improve the traditional GM(1, 1)model and then used the concept of equal dimension and new information to update the data sequence required for modeling. The model was used to predict the water quality status and water quality evolution trend of Nansi Lake from 2019 to 2021. The results show that the grey Markov water quality model has small relative errors, high accuracy and reasonable prediction results. From 2019 to 2021, the overall water quality of Nansi Lake will gradually improve from north to south, wherein the mass concentration of COD_Cr, NH₃-N, and COD_Mn shows a downward trend while the mass concentration of TP and TN has an upward trend and there is a risk of exceeding the standard. Therefore, the control of TP and TN in the Nansi Lake Basin should be strengthened.