Abstract: Liaohe Oilfield mainly produces heavy oil. The oil is pipelined from oil well to complex station for dehydration processing. However, the sediment tank structure and oil/water velocity field are different, which result in the fluctuation of temperature field to bring out a lower dehydration rate. By adopting FLUENT software and establishing the temperature field model of the sediment tank, the velocity field is divided into the liquid inlet zone, sediment zone and oil gathering zone to analyze the settlement/separation effectiveness and temperature field differences at inlet temperature of 60 ℃、70 ℃、80 ℃、85 ℃. The numerical study shows that the water layer depth in sediment tank increases with time; below the inlet pipeline of sediment tank there is no obvious oil layer in calculation time. At the low temperature zone of sediment tank, the heavy oil is highly viscous and hard for dehydration.