Based on the principle of mass balance, a dynamic forecasting model of CO2 concentration of sunlight greenhouse in the northern drought cold area was established. The influenced factors correlative with CO2 concentration changing such as crop photosynthesis and respiration, soil respiration, carbon dioxide supply and natural or winded of closed situation ventilation were established in the model. To validate the correctness of the model, an experiment was carried out in a sunlight greenhouse in Agricultural Science and Technology Park in Inner Mongolia. The results showed that the inner forecasted CO2 concentration was well consistent with the measured data under the condition of sunny or cloudy day in the northern drought cold area in winter, and the relative error was less than 10%.