This paper proposed a simulation model for analyzing interoperation process of road autonomous transportation system. First, an interoperation simulation model built with complex network theory is proposed. In the model, vehicles and infrastructures are modeled as nodes of graph. Then, a network evolution model based on random graph theory is proposed. The network evolution model aims to create interoperation topology between vehicles and infrastructures. An autonomous level transition algorithm is subsequently proposed. In the algorithm, interoperation and information sharing is considered as key components of influencing autonomous level, where age of Information (AoI) is the pivot indicator of validity of the shared information. The paper conducts a case study in highway scenario for validating effectiveness of the model. In the case study, the proposed model is further utilized to analyze the pathway for upgrading autonomous level via interoperation. The result of case study showcases the proposed model can characterize relationships of interoperation and autonomous level. The proposed model offering a theoretical basis for foundation of interoperation link in road autonomous transportation system.