The passive solar house is one of the effective techniques to decrease the energy consumption of buildings. In this paper, the ventilation performance of synthetic solar house with sunshine room has been analyzed, while it is used as auxiliary ventilation in summer. The mean temperature of air in this room is calculated through the model of heat transfer of solar room, and then the auxiliary ventilation quantity is calculated. It is concluded that the capacity of auxiliary ventilation of synthetic solar house can meet the fresh air demand of common residential construction, but if there are more ventilation quantity needed the capacity of auxiliary ventilation of synthetic solar house is insufficient. The simulation calculation provides the necessary theoretical basis for the further theoretical and experimental research on synthetic solar house.