As for the current data center, IT equipment heat generation is increasing. Therefore, it is possible that the issue for IT equipment cooling cause. High heat generation of IT equipment that bring a big change in thermal environment in server rack. In some case, it may cause the failure of server, and it may cause an efficiency of IT equipment cooling decrease whole room. In this study, we evaluated the phenomenon by modeling of IT equipment cooling and laboratory experiments. And we evaluated the influence of thermal environment in server rack, by high heat generation of IT equipment and layout in the server rack. In this article, I would like to describe that the thermal environment in server rack and IT equipment cooling efficiency are affect by high heat generation of IT equipment. In addition, I would like to suggest the method of IT equipment cooling in data center in the future.