Abstract: To determine water cut rising law of low-amplitude heavy oil reservoirs with bottom water in horizontal wells, the paper considers dynamic and static parameters, uses a comprehensive method combining numerical simulation, waterflooding type curves with production performance analysis, and summarizes the order of influences of different parameter on water cut variations in reservoirs with bottom water in horizontal wells. Linear regression equations related to each parameter are obtained and a chart showing water cut rising in horizontal wells is established. Based on the comparison of production performance data in horizontal wells with that of Q oilfield in the middle of Bohai Sea, it is considered that the method has relatively high prediction accuracy, which could provide basis for production system adjustment in horizontal wells, meanwhile provide theoretical basis for horizontal well production allocation at the early stage