The light illuminance and thermal environment of the internal space were simulated with the software of ECOTECT to acquire the influence of the balcony design to the indoor physical environment in the design stage of the residential buildings.Then the indoor lighting coefficients,the change of indoor temperature and heat hourly in the different design scheme were compared.The results show that the software of ECOTECT can be used to simulate the influence of the balcony light and heat on the indoor environment,which provide a good reference to the balcony design.