Cyclic steam stimulation(CSS) is currently the most common production method in heavy oil reservoir. Its main mechanisms are formation elastic energydriven, crude oil viscosity reduction by heating, improvement of oilwater relative permeability, liquid thermal expansion and plug removal of near wellbore area. But the contribution of the mechanisms of cyclic steam stimulation is rarely discussed. By using reservoir simulation software and orthogonal test analysis, how to realize CSS simulation was described by the current popular thermal recovery numerical simulation software, and showed that the importance sequence of these five kinds mechanisms contribution on CSS recovery was as follows: formation elastic energy, crude oil viscosity reduction by heating, plug removal of near wellbore area, liquid thermal viscosity and improvement of oilwater relative permeability. And the previous two played a decisive role, which were the high recovery guarantee of CSS. Research findings could guide designers to efficiently design CSS in heavy oil reservoirs and to use simulation software for CSS.