Abstract: The retention effect of reservoir on nitrogen is an important influence factor on the eutrophication prevention and control. In order to reveal the differences of nitrogen retention characteristics and the influence factors at multiple timescales, an ecological dynamic model was developed in Shanmei Reservoir watershed. Based on the retention flux and retention rate calculation, the nitrogen retention effect was analyzed at three time scales of yearly, monthly and daily, respectively. Furthermore, multiple linear correlation analysis was conducted to analyze the influence of inflow runoff, ratio of inflow to outflow, residence time, velocity and temperature on the retention of nitrogen in the reservoir. The results showed that the process of nitrogen retention always displayed fluctuant characteristic at different time scales. On a yearly scale, the reservoir mainly played a role of nitrogen sink; on a monthly scale, seasonal variation of nitrogen retention and release effect made the reservoir as nitrogen sink in wet period and as nitrogen source in dry period; on a daily scale, the nitrogen retention process fluctuated intensely, with the retention rate ranging from -300% to 100% in dry year. At different time scales, ratio of inflow to outflow and velocity were always the important factors to affect nitrogen retention in the reservoir, with significant correlation coefficients consistently. With the time scale changing from yearly to monthly, daily, the influence degree of inflow runoff and temperature on nitrogen retention was gradually strengthened. The correlations between the residence time and retention rate could be positive or negative at different time scales.