Abstract: Industrial parks usually have onsite energy supply systems, which can regulate the electricity generation to participate in the ancillary service market. Before providing the ancillary service, facility owners need to evaluate the flexibility to ensure the energy supply security. In order to accurately evaluate their own flexibility and reduce the conservativeness of traditional robust optimization methods, a flexibility boundary solution framework based on adjustable robust optimization is proposed. Firstly, referring to the requirements of existing flexibility services to industrial sites, we developed a multi-energy coupling model of energy supply system in industrial park, and proposed the corresponding evaluation indices. Then, taking the state uncertainty of the energy supply system in industrial park into consideration, we proposed an adjustable robust optimization model based box uncertainty set. By introducing conservativeness parameter into the model, the flexible regulation of the flexibility boundary can be realized. The framework is applied to the energy supply system in an industrial park. The results show that the proposed framework can adjust the conservativeness of flexibility boundaries considering the conflict of incomes from flexibility provision and penalties for default to provide services on demands.