Agent organization is an important research topic of MAS (multi-agent systems). The explicit expressions of Agent organization structure are more widely used in the implementation of Agent organizations. A formal semantics of processes of Agent organization structure design is given in this paper based on p-calculus and the chemical abstract machine (CHAM). Components associated with the organization structure design are taken as molecules of CHAM and use the executions of the CHAM to express procedures of Agent organization structure formation.This formal semantic method is both accurate and direct.It is convenient to implement Agent organization structure design and improves the work of Ferber and Xu about implementation and semantics of Agent oranization and organization structure.