According to CFD (Fluent), a gas flow and heat transfer mathematical model was adopted for the certain process parameters of a new carbon dioxide incubator. The unsteady numerical simulation of its internal flow, heat transfer in the doorway was done. The impact of opening and closing door was discussed. The results showed that: ① The effect of outside air on the internal temperature after opening the outer door for 5s’ period of time has been small; ② The affected areas of the temperature in the incubator are from the doorway to the interior, from the downside to the upside, from the left wall on the side of the opening position to the right wall on the side of the open door in 25s’ period of opening door; ③ After closing the outer door, the temperature of the areas near the back wall and the right wall make a good recovery, the temperature of a certain region near the door is more difficult to restore.