The hourly usage ratio is very important for lighting and equipment energy predicting of office buildings and energy saving calculation of energy efficient retrofit. 17 office buildings in Chongqing were selected to calculate daily usage ratio by using whole-year electrical consumption data of lighting and equipments energy system. According to the different hourly usage ratio, office buildings have been categorized into two main types by using cluster analysis method. Then, the typical hourly usage ratios of two types of office buildings were calculated.