Palestinian schools are designed due to the standards of ministry of education (MOE) in cooperation with UNESCO. Local school building designs are required to be more efficient climate-based and energy-conscious while maintaining indoor comfort levels. In addition, these schools suffer from classroom high occupancy density of up in the Gaza Strip to 40 students, while the target value is 30 students per classroom.   The paper aims to study the effect of occupancy, orientation, and window to wall ratio (WWR) factors on total energy consumption of school buildings in Gaza, Palestine and optimized the best for minimum energy use intensity.The method started by analyzing local climate and defined the reliable weather data for the software. A simulated model, that presented the common existing school building situation and located at Gaza strip, was developed. This model results was set as a reference value. The study investigated the effect of changing the occupancy density rates with considering international and local standards,orientation at the four basic directions, and WWR with regards to its impact on the amount of HVAC loads and lighting energy demand for the building. These investigations will optimize the best occupancy density and window size on energy consumption.    The results indicated that the increasing of occupancy had significant effect rather than opaque and glazing on energy consumption. It showed that density use in school buildings affect energy use about (27%) above the international standard, where the building envelope characteristics still determine a large part of the energy use in a school building (37.5%) for HVAC and lighting loads. East orientation has more effect on increasing energy consumption than other orientations as a result the amount of exposure to solar radiation for a longer period of the western façade due to the school schedule.