Abstract: This paper bases on hydrology and hydraulic characteristics to simplify convection disperse functions reasonably and gives a dynamic analytic solutions under instantaneous suddenly draining sewage conditions.This paper also develops a river water quality model with arid region characteristics including three basic water quality factors,carbonized BOD₅,ammoniated nitrogen,and dissolved oxgen,deduces a water quality modeling matrix,and applies it to simulate and estimate the water quality dynamic process in the Shui Mohe River in the arid Urumqi region.