Scenarios are the basis of virtual simulation and should be properly designed and created to ensure the diversity, rationality and criticality. Many researches involve the description of scenario and generation of test case. In this work, we propose a new SOTIF scenario hierarchy to depict static entities, dynamic information and relationships in the scenario. The concept of scenario potential risk is defined in this paper. The prior collision probability and safety control intensity are introduced to quantize the scenario potential risk. Finally, based on the architecture of scenario, we designed a novel process to automatically generate scenarios with the genetic algorithm. The experiments carried out show that proposed methods can generate diverse and trivial test case library.