The causes of the performance gap between the predicted energy demand and actual End Use Energy Demand (EUED) are seen to be underpinned by two main issues. The first issue is the assumptions for the modelling tools in term of physical attributes of buildings, building system and occupants. The second issue, which is more problematic, is whether the given inputs to the modelling tools are realistic or not, in particular, business requirements (fixed or flexible schedules), occupancy (level, pattern & behaviour) and Building Management System (BMS) which can be overly simplified and are unable to address the dynamism between factors within buildings. This over-simplification (often necessary to run the model) is seen the major cause of the performance gap. In this paper, the authors attempt to address one of the issues with regards to the occupancy in large public buildings with significant people movement, such as subway station, museums, public library. The traditional approach is using statistical benchmarking data to establish the basic occupancy schedule, such approach is often not reliable and doesn’t reflect the operational reality which is dynamic and unpredictable. However, the challenges of dynamics of people movement have been tackled in the other areas such as crowd modelling and people moving analysis. Techniques and tools have been developed to simulate people movement in different environment. This paper proposes an approach of employing people movement modelling technique to simulate the occupancy in public buildings.