A model was developed to predict the effects of rising air temperature on net photosynthetic rate of Quercus mongolica stands at Mt. Paekcheok-san, Kangwon-do in South Korea. The PFD (Photon flux density) and air temperature were determined from weather data from the research site and the Daegwallyeong meteorological station and gas exchange or release responses of each tree component were measured. Using these data, we simulated the effects of increases in mean annual air temperatures above current conditions on annual $CO_2$ budget of Q. mongolica stands. If mean annual air temperature is increased by 0.5, 1.0, 1.5, 2.0, 2.5 or $3.0^{circ}C$, annual net photosynthetic rate will be increased by 8.8, 12.8, 14.5, 12.6, 9.2 and 1.0 ton $CO_2;ha^{-1}yr^{-1}$ respectively. Simulations indicate that changes in air temperature will have a major impact on gas exchange and release in Q. mongolica stands, resulting in a net increase in the rate of carbon fixation by standing crops.