Modeling and analysis of patient flow in hospital emergency department (ED) is of significant importance. In a hospital ED, the patients spend most of their time in the patient room and most of the care delivery services are carried out during this time period. In this paper, we propose a system model to study patient (or work) flow in the patient room of an ED when the resources are partially available. A closed and re-entrant process model is developed to characterize the care service activities in the patient room with limited resources of doctors, nurses, and diagnosis tests. Analytical calculation of patient’s length of stay in the patient room is derived, and monotonic properties with respect to care service parameters are investigated.