As the core of intelligent manufacturing, CPS has serious security issues, especially for the communication security of its terminal M2M. In this paper, blockchain technology is introduced to address such a security problem of communications between different types of machines in CPS. According to the principles of blockchain technology, we design a blockchain for secure M2M communications. As a communication system of M2M consists of public network areas, equipment areas and private areas, we design a sophisticated blockchain structure between the public area and private area. For validating our design, we take cotton spinning production as a case study to demonstrate our solution to M2M communication problems under the CPS framework.