The different sequences of the coupled tasks set lead to different development cycles, so optimizing sequences is a key for reconstructing complex product development process. As there are overall iterations stemming from activities’ coupling in complex product design process, this paper first proves two propositions of ordering coupled tasks by stochastic process theory: 1) more shorter the development cycle of a coupled activities subset is , more shorter the development cycle of the entire coupled activities set is. 2) If the execution sequence of the coupled activities set is changed, the development cycle of the coupled tasks set will also change. When execution order of two activities is converted into partial order of two elements, this paper presents a sequence optimization algorithm based on qualitative and quantitative partial order (SOQQ) from these two propositions. Simulation has been used to confirm SOQQ algorithm’ validity and high efficiency.