Two cities located in cold zone, Lanzhou and Zhengzhou were selected to study the relationship between the building envelope properties and the building heating and cooling load.Under the condition of energy efficient rate 65%, four types of walls, three types of windows and four window-to-wall ratios were assembled into 48 types of office building envelopes as the calculating rooms. The annual heating and cooling loads of the calculating rooms were obtained and the influence of thermal performance on building load was analyzed. The energy saving ratio and the optimal building envelope for each city were determined by comparing with the annual total load of baseline room,.