A simulation model of stem growth of tomato in long season cultivation in solar greenhouse was developed based on the Ecophysiological Processes of tomato organ. The foundation on which Simulation Model of leaves and fruit of Tomato would be built was the simulation model of stem segments. The varieties were Caruso and Carter Linna applied to long season cultivation in solar greenhouse. Some parameters such as maximum rate of node initiation were calculated or given. The results showed that the simulated and observed data of tomato stem were agreeable and the average relative error was 0.7%-9%. The correlation coefficients between simulated and observed data were 0.9964 and intercept was -8.8 in scatter chart, which meaned the simulated data was lower than the abserved data by 8.8. So the model has good performance.