For reaching the requirement of process domain, a flexible and formalized process modeling language FLEX is proposed to support semantics richness, easy of use, flexibility, scalability, reuse, and distribution, while it is analyzable, executable, and evolutive. Especially, the language not only can provide nonexperts high level representation for easy of use, but also can allow users to define and reuse process notations at various granularities to extend the representation. So FLEX can support various levels and requirements of process modeling.