Background: Hospital congestion is a common problem for the healthcare sector. Numerous studies explored reasons for crowding within some parts of the hospital. However, to deal with more general, hospital-wide problems, examining the hospital as a connected whole is necessary. The purpose of this study was to evaluate de-congestion interventions through a whole hospital simulation model and offer objective reasoning to support hospital management decisions.Method: This study tested a congestion prevention method that estimates the current day’s hospital congestion risk level R at a set time every morning, and activates minimum intervention when R is above certain threshold R(C), using a virtual hospital created by simulation modelling. The color-coding system was adopted to demonstrate the impact and the extent of effectiveness of this method in preventing hospital congestions.Results: The results indicated that adding 8 flex beds to the medical department resulted in more reductions (70.93%) of red-days comparing with the surgical ward (37.15%). Red days reduction per affected patient when discharging two medical patients was 0.1 which was higher than when discharging two surgical (0.04) or two long-stay patients (0.07). Also, the efficiency of red days reduction per affected patient is always greater if removing 2 patients than if discharging more patients. Conclusions: The expected outcome based on theoretical prediction of this method was confirmed, that is, applying a less disruptive intervention is often enough, and more cost effective, to reduce the risk level of hospital congestion. Making a small number of extra beds available was a superior solution compared to discharging approaches to reduce crowding in hospitals. In addition, the virtual implementation approach enabled testing of the method at a more detailed level, thereby revealed some interesting findings difficult to achieve theoretically, such as discharging extra two medical inpatients, rather than surgical inpatients, a day earlier on days when R>R(C), would bring more benefits in terms of congestion reduction for the hospital.