Based on the overall vision of the Sixth Generation Mobile Communications (6G) and the different dimensions of the sub-vision, the article outlines key technology trends and challenges that are likely to achieve these wonderful visions. This article is based on new basic technologies such as new composites, meta-materials, non-orthogonal waveforms, high-frequency millimeter and terahertz waves generation, to network-based technologies such as wireless new Internet infrastructure and deep-sea communication networks. Emerging application technologies such as perceptual interconnection and human body communication are introduced in different categories to select key technologies that are full of opportunities and challenges in the 6G era. This article cites the relevant content and research results of some of the top international academic journals, and strives to be as rigorous and reasonable as possible, with a view to attracting industry attention to the development trend of 6G mobile communications.