The thickness of three-dimensional carbon fiber preforms is a key factor in the design and processing of carbon fiber composites. However, there is no corresponding national standard for its measurement method, and there are significant differences among different testing methods. The existing thickness measurement methods of three-dimensional carbon fiber preforms are summarized and analyzed. The principle, advantages and disadvantages of non-destructive thickness measurement methods are mainly introduced. It is proposed that non-destructive testing should be taken as the research and development direction of thickness measurement methods for carbon fiber three-dimensional preforms.