In this paper, with the view that software process (SP) is a software too, we first discuss notations of its control and data structures. Through analysing the process model and its macrostructure, we present the construction principles of process model and three kinds of elementary control structures, i.e. , regular structure, backtrack structure and parallel structure; On the basis of the above, we analyse the complexity of SP and discuss the completeness of expression. Finally we show some instances of control of contril structures and control flows through describing activies during sP and activities in JSD methodology.