Abstract The software DeST-c is used to analyze the influence of window type,window-wall ratio and sunshade coefficient on the building total load index of an office building in Lanzhou. The results show that the building total load indexes in differentdirections are linearly increasing with different growth amplitude when there is no internal sunshade. The southern total load index has the minimum value while the western has the maximum value. The internal sunshade has different effects on energy-saving rate in different directions. The total load index in southern direction is decreasing with the increasing window-wall ratio while the variation tendency of the total load index in eastern direction and western direction is consistent with that when there is no internal sunshade. The variation of the window heat transfer coefficient has more significant effect on total load index in south orientation than that of the glass sunshade coefficient.