Building an accurate energy-consumption model of servers can assist resource providers in predicting and optimizing energy consumption of data center. To address the problem of low accuracy of energy consumption model caused by the failure to consider "load characteristics" of servers in data center, a new energy consumption model and quantitative calculation method are proposed in this paper. The main ideas are summarized as follows: Firstly, we divide the tasks into three classes: CPU intensive task, transactional web task, and I/O intensive task. Then, energy consumption contributions of all components in a server are analyzed. After that, the dominant component parameters of server energy consumption are chosen by using the Principal Component Analysis （PCA）, to build a power model through the multiple linear regression method and non-linear regression method. Experimental results show that the prediction accuracy of the proposed energy consumption model can achieve more than 95%. Compared with other energy consumption models, the accuracy can be improved by around 3%.