Digital twin, as the key technology of cyber-physical system, can digitally describe the physical world and effectively manage and control the data of the entire product lifecycle, and provide new ideas to optimize the various activities in product research and development. The concept and research progress of digital twin is discussed, aiming at the two problems existing in the current CAPP (Computer Aided Process Planning) research, the concept of as-build model is introduced, the design framework of CAPP under the digital twin is proposed, and finally a real-time process decision-making method based on digital twin and a process knowledge mining method based on digital twin are discussed.