The Industrial Internet is a promising technology combining industrial systems with Internet connectivity to significantly improve the product efficiency and reduce production cost by cooperating with intelligent devices, in which the advanced computing, big data analysis and intelligent perception techniques have been involved. This paper comprehensively surveys the recent advances of the Industrial Internet, including reference architectures,key technologies, relative applications and future challenges. Reference architectures which have been proposed for different application scenarios and their corresponding characteristics are summarized. Key technologies, such as cloud computing, mobile edge computing, fog computing, which are classified according to different layers in the architecture, are presented to support a variety of applications in the Industrial Internet. Meanwhile, future challenges and research trends are discussed as well to promote further research of the Industrial Internet.