In present energy conservation design, air-conditioning operation is deemed to be continuous in the whole building, but the intermittent operation of air-conditioning is widely applied due to the occupant's behaviour. The large discrepancy in the energy efficiency and energy consumption can cause between the actual usage and the primary design. Considering this situation, a numerical simulation was carried on to optimize the thermal performance of non-transparent envelope components in three typical rooms with air-conditioning under the intermittent operation in summer. The energy-saving potential of all components was analysed, while the whole heat transfer capacities in three typical rooms were compared between traditional and optimized envelopes. Results showed by optimizing envelope components, the average heat flow values could be reduced by up to 13.78-71.27%, while the average heat transfer capacities were reduced by 33-39% and their fluctuation percentages were also decreased obviously. Compared to interior and exterior walls, floors and ceilings had the higher energy-saving contribution percentages of 35-80% and the larger the room area, the larger the energy-saving contribution percentage of floors and ceilings.