Nowadays Internet of Things (IoT) is a major paradigm shift that will mark an epoch in communication technology such that every physical object can be connected to the Internet. 5G makes a significant breakthrough in the traditional mobile communication system and support the applications of IoT in various fields including business, manufacturing, health care and transportation.5G is increasing the service capability of future IoT and operates and connects the whole society. 5G is facing enormous challenges when it supports differentiated applications with a uniform technical framework. In recent years, Artificial Intelligence (AI) is rising to these challenges with the rapid development. It is a potential solution to the problems in the 5G era and will lead to a revolution in the capabilities and concepts of the communication systems. Many researches have already been done for applying AI in 5G. In this paper, we focus on clarifying the promising research directions with the greatest potential rather than trying to review all the existing literatures. In this research, 5G can be anticipated to achieve significantly better performance and more convenient implementations compared to the traditional communication systems. With the inspiring research paradigms introduced in this paper, we are looking forward to the remarkable achievements of AI in 5G in the near future.