Abstract: The diurnal variation models of photosynthetically active radiation ( PAR) , air temperature ,CO² concent ration and leaf photosynthesis of tomato in greenhouse was developed under three conditions , fine day and no ventilation , fine day and ventilation , cloudy day and no ventilation in winter and spring. The simulated values were compared with the observed values , and the result s showed : ①On fine day and no ventilation , PAR , air temperature and CO₂ concent ration were well simulated , photosynthetic rate was well simulated in the morning. ②On fine day and ventilation , air temperature and CO₂ concent ration were well simulated , but the simulation of PAR did not fit well with the observed values because of the effect of the diurnal variation of radiation t ransmission coefficient of air or transmittance of film , however , photosynthetic rate was well simulated. ③On cloudy day and no ventilation , the simulation of air temperature and CO₂ concent ration
were slightly higher than the observed values. There were some differences between the simulated and observed values of PAR , but the tendency of the simulation values of photosynthetic rate and PAR were the same. The effect of PAR on photosynthetic rate on cloudy day was verified. The research results will be helpful for developing the model of tomato growth and guiding production in greenhouse.

Key words: Greenhouse, Tomato, Weather factors, Photosynthesis, Simulation model