Taking a new type of complex electro-optical system as the research object, in order to address the shortcomings of poor objectivity and large allocation deviation in traditional scoring allocation method, an importance correction factor was constructed, and a reliability scoring allocation method introducing importance correction factor was proposed. Firstly, the fuzzy analytic hierarchy process was used to obtain the relative importance of the impact of functional units on the reliability of superior functional unit or system. Then, based on the relative importance, the absolute importance of the impact of functional units on the reliability of superior functional unit or system was obtained according to expert scoring rules. Finally, based on the relative and absolute importance, a functional unit importance correction factor was constructed to correct the scoring results of each functional unit. After verification and comparison, the reliability allocation value of critical functional units is at least 6% higher than the traditional scoring allocation value, and the scoring allocation method introducing importance correction factor can effectively weaken the subjective impact of the traditional scoring allocation method, release the reliability margin of critical functional units, improve the scientificity and rationality of reliability allocation of functional units, and thereby improving the reliability design level of complex systems.