The traditional function decomposition can decompose the total function of products to the function-unit. It puts each function-unit having a certain solution as a symbol of the end of traditional functional decomposition. The method of traditional function decomposition emphasizes that the total function could be decomposed into several functional-units, in turn, several functional-units constitute a total function, which reflects the linear and reducibility relationship between the total function and the functional-unit. The traditional function decomposition can’t reflect the characteristics, such as nonlinear, time-varying characteristics, openness, functional coupling and so on. Therefore, it is urgent to need a kind of functional decomposition process model for complex electromechanical system. Firstly, there is an integration of the design-centric complexity (DCC) and TRIZ. According to the results of preliminary function decomposition and TRIZ theory, it is divided into effective complete function and non-effective complete function. Secondly, it puts forward the function of average probability method and function realization probability extremum method and builds relationships between the effective complete functional classification of TRIZ and the repeat function and combination sets of DCC theory. Through transformation of TRIZ, the repeat feature sets, combination sets of system and composite auxiliary function sets are put as the result of functional decomposition of complex electromechanical system. Functional decomposition process model for complex electromechanical system by DCC theory and TRIZ integration was formed. The model of the design process was verified with an engineering example.