Abstract: Based on the homogeneous flow model, the mathematic model of optimization of inside rifled tube under non-uniform heating condition which included horizontal flow, inclined upward flow, vertical upward flow and vertical downward flow was established. The two-phase flow instability was simulated by the time-domain approach. With the same parameters as the Siemens, the variation of inlet flow rate with time was obtained. It is shown that the results have a good agreement with those of the Siemens. Therefore, the mathematic model and numerical method were reliable to simulate the two-phase flow instability. The parametric effects on the two-phase flow instability under non-uniform heating condition were analyzed and compared with the effects under uniform heating condition. The results show that they are similar to those under uniform heating condition, which indicates that increasing inlet pressure or inlet flow rate will improve the system stability, and decreasing the inlet pressure drop coefficient or increasing the outlet pressure drop coefficient will reduce the system stability.