Three kinds of climate change simulation devices are used for study elevated CO_2 concentration and air temperature increase:1)Open system:Free Air CO_2 Enrichment (FACE) with Infrared Heating(IH);2)Half-open system: Open-Top Chamber (OTC); 3)Close system: Environment Chamber(EC). But the extremely high hardware and running cost of FACE and IH are the main restricts for their application. EC system cannot represent the really condition with large extent of crop growth environment change. Traditional OTC system with much lower cost has nearly the same growth condition for crop, but it is a passive temperature increasing system and has no CO_2 addition. To well use the advantage of Half-open OTC technique for climate change simulation, we improved the traditional Open-Top Chamber (OTC) device by adding heating module, CO_2 injection module and air exchange module. A hexagonal OTC was designed with 1.2m side length and 2.5m height, and the CO_2 tank used for CO_2 injection source and semiconductor sheet sealed for the heating system. Air heating and CO_2 injection were automatically controlled when pumping outside air into OTC by fans to simulate the elevated air temperature and CO_2 concentration scenario. We applied the improved OTC in early rice season, and the OTC was emplaced in the real rice paddy field without obstacle at the bottom for water supply. And air temperature, humidity and CO_2 concentration were measured by every 2 min. The results showed that the difference of daily mean deviation of air temperature of the controlled OTC and the objective simulation temperature can be controlled less than 0.2℃ with the largest difference of -0.58℃, and the controlled deviation of CO_2 concentration was-39.4~4.8muL/L. This research indicated that the improved OTC can be applied to simulate the elevated air temperature and CO_2 concentration of the future climate change scenario. Meanwhile, the relative humidity in improved OTC is also showed that relative humidity (RH) nearly has no change without temperature increase, and would increase by 2% if air temperature increased. In a word, this improved OTC device can be used to simulate elevated CO_2 concentration and air temperature of early rice for climate change simulation research.