An analysis method based on grey target theory is proposed to solve the problem deals with key technology contribution rate of weapon system of system (WSoS). Firstly the WSoS hierarchical structure is elaborated and mapping from system to technology is established. Secondly technology contribution rate is defined to describe the contribution rate for a system to function and WSoS to fulfill its mission and the analysis process of technology contribution rate is illustrated. Then the grey target theory is applied to quantify technology contribution rate. Finally the appliance of the method proposed is demonstrated by a WSoS case study. This method can be applied in creating the WSoS technology planning rules and supporting WSoS development and decision-making.