Because of the increasing power density of IDC, the backup of the refrigeration system is becoming more and more important. Once the power system failure, the servers can continue to run on the UPS system. After the refrigeration system stops running, the room temperature will rise rapidly, and the servers will be overheat and stop running. The equipment maintenance method and operation errors may also have a greater impact on the data center air conditioning system. In this research we analyze the temperature increase when the cooling system lost power in high power density data center and the influence to the IT servers in IDC rooms. According to the research results, we put forward some effective suggestions for the design of refrigeration system and maintenance methods.