With the rapid development of traditional energy system, the essential obstacles to the coordination between different energy sources is increasingly obvious, which greatly hinders the further improvement of energy efficiency. As a promising energy supply and consumption system, Regional Energy Internet (REI) has significant practical values in improving the coordination of traditional energy and promoting large-scale renewable energy penetration. Due to the large scale, high ambiguity and numerous key interactive criteria, the investment decision making of REI project is a key problem in application management, but it is challenging and has not been solved. Therefore, this paper explores a targeted and scientific REI investment decision making framework through the interval type-2 fuzzy number, Choquet integral and fuzzy synthetic evaluation model according to different preferences of investors to ensure the successful implementation and effective resources integration of potential REI projects. To verify the effectiveness of the framework, a case study with three typical REI projects simulated from a two-stage stochastic optimization model is studied, and corresponding investment countermeasures are proposed as a reference to allocate resources and prevent risk. Besides, since REI investment decision-making has not been deeply studied, this paper contributes to literature and expands knowledge.