This paper addresses a robust and nonblocking supervisory control problem based on a framework of discrete-event systems with model uncertainty under partial observation. The uncertainty introduced in this paper is associated with internal and unobservable events occurring in systems. This paper presents a systematic method for modeling uncertainty described as a Delta -transition representing the internal and unobservable events. In particular, at a state with the assigned positive integer value p a system is assumed to experience at most a p-step state transition by the internal and unobservable event. Under the framework on model uncertainty, this paper presents necessary and sufficient conditions for the existence of a robust supervisor with the nonblocking property.