Abstract: Offshore heavy oil is an important source for the increase of crude oil production in the future, but compared with land oilfields, the gathering of offshore heavy oil is more challenging due to low temperature environment and riser transportation. Lifting heavy oil with water annulurs can significantly reduce the transporting friction, so it is a very promising way for the cold-transportation of heavy oil. Based on the theory of oil-water two-phase flow and computational fluid dynamics, the geometrical and mathematical models of the vertical upward heavy oil-water central annular flow (CAF) are built by using FLUENT 6.3.26 and GAMBIT 2.3.16 software, and the validity of this model is discussed. The flow regime and features of vertical upward CAF are simulated and analyzed, and the influences of the width of annular gap in different water annulurs generators and flow velocity of oil-water on the vertical upward CAF are discussed. The results show that when the ratio of flow velocity of oil to water is in a certain range, the simulation result of vertical upward CAF by this model is in good agreement with the experiment result. Vertical upward CAF can maintain ideal central annular flow at the entrance and has a smooth oil-water interface, but the oil-water interface begins to fluctuate as the oil and water rise up together. The width of annular gap in water annulurs generators has a great impact on the vertical upward CAF and if the width is too small, the stability of water annulurs will be poor and the flowing friction will be high, while on the other hand, if the width of annular gap is too big, oil output will be too small. Considering the both of energy consumption and oil output, the efficiency of oil transportation is the highest when the width of annular gap in water ring generator is 1.8 mm under the simulation conditions.