In order to solve the unstability of the core-annular flow in the transport of high viscous oil, this paper proposed a new core-annular flow generator, and explored the stability characteristics and optimization research of generator transmission characteristics. To simulate the core-annular flow under the condition of different thickness and to improve the stability characteristics by using spiral blade, the VOF model was used to simulate the flow. A numerical model of core-annular flow according to the principle of core-annular flow forming was established, and the correctness of the numerical model was verified by comparing the experimental results. The results show that the formation and stability of core-annular flow is not conductive when the thickness of the gap is too large or too small, and when the flow rate is 1 m/s, the core-annular flow generated by the generator gap of 1.4 mm in the pipe with the diameter of 19 mm is more stable, which means that when the ratio of the gap thickness to the diameter of the main pipe is 3∶20, the most effective result is observed. The use of helical blades can increase the stable length of the core-annular flow from 150 mm to 500 mm with an increase of 2.3 times.