Abstract: Potatosunflower intercropping is a prevailing cropping system in the agricultural and pastoral ecotone in China. To precisely simulate the crop phenology in the intercropping system is of significance for the assessment and optimization of intercropping systems. In this paper, the simulation model for the development stages of sunflower and potato in monoculture and intercropping was established, based on the crop’s physiological development time, and validated with the field experimental data from 2010 to 2011. A good fitness was observed between the simulated and observed values of the crop’s development stages. The root mean square error (RMSE) of the development stages from sowing to emergence, emergence to flowering, flowering to mature, and from sowing to mature was 1.2, 2.9, 2.4 and 2.6 d, respectively, with the prediction error lower than 5%. The model was strong on mechanistic, explanation and adaptability, and could be applied as a good tool in the researches of crop growth and development.