Chemical oxygen demand (COD) is one of the major indicators of surface water pollution in China. Degradation coefficient of pollutant may provide scientific basis for understanding the process of organic polluter change and effective pollution control. As a typical urban river recharged with reclaimed water, Beiyun River is at very serious state of COD pollution. In this research, five typical sections from upstream to downstream (Mafang Bridge, Huosha Road, Dongguan Bridge, Yulinzhuang Bridge and Yangwa Sluice) on Beiyun River were selected for estimating COD_Cr degradation coefficients and calibration by laboratory simulation experiments. Taking the section of Yangwa sluice as a typical example, the sedimentation rate and reoxygenation coefficient were measured on site to evaluate water self-purification ability. Then the impacts of different environmental factors (temperature, dissolved oxygen and flow rate) on COD_Cr degradation were discussed based on laboratory simulation experiments. The conclusions were summarized as follows:The water purifying ability of Beiyun River was very low. The sedimentation rates ranged from 1.59 to 3.22 m/d, among which, the lowest rate was in Yangwa Sluice with a reoxygenation coefficient of 0.016 d^-1. The variation of COD_Cr degradation coefficients conformed to the first-order kinetic equation, ranging from 0.0184 d^-1 to 0.0883 d^-1 corrected by the hydraulic and temperature condition. The COD_Cr degradation coefficients showed significant spatial variation. The degradation coefficients of upstream sections was higher than that of downstream sections, except Yangwa Sluice (last section of Beijing at downstream) as the highest (0.0416-0.0883 d^-1), showing the characteristics of the sluice. Water quality parameters such as temperature, dissolved oxygen, redox potential (ORP), nutrients, and total organic carbon (TOC) were the main influence factors. The COD_Cr degradation coefficients increased with the temperature, dissolved oxygen and flow rate. In addition, COD_Cr degradation coefficient was positively related to nutrients and TOC, but negatively to ORP. The results of this study can provide a scientific reference for urban river improvement and pollution control.