Abstract: With the rapid development of cloud computing and virtualization technology, the number as well as the scale of data centers are growing rapidly around the world, which results in huge energy consumption of data centers. At the same time, however, the resource utilization of data centers are very low, leading to a lot of waste of energy. Due to the contradiction between huge energy consumption and extreme low resource utilization in data centers, optimizing the energy efficiency of data centers has become a hot topic in both academic and industrial fields in recent years. Aiming at the basic problem of energy efficiency in data center, we study the key technology of energy saving in data center based on resource and task scheduling. From the view of energy efficiency model and energy efficiency algorithm, the research progress and the latest achievement of energy efficiency in data center are summarized, mainly on server system and network system. This paper firstly decomposes and analyzes the data center energy consumption sources. Then the typical energy consumption models and classification standard are introduced. Based on the models and the standard, the strategy algorithms are summarized. The development trend of energy efficiency optimization in data center is also prospected.