Passive architectural design is an effective strategy for affordable housing in the developed countries. The importance of passive design comes from improving indoor comfort with low cost, low maintenance, high reliability and environmental psychology effects. The difficult climatic conditions of deserts regions consider a challenge for using passively treated housing significance, simulates the indoor environment conditions are good examination for its feasibility. This research aims to study the indoor environmental adaptation capacity with the extreme outdoor conditions of desert climate. The study selects one of low-cost housing projects developed by private sector in Cairo desert; Haram-city is a new existing community located in 6th of October city and has about 70.000 housing units. Haram-city housing design is based on passive design approach of desert climate such as thick walls, low window-wall ratio, domed and vaulted rooftop. The research use digital simulation software to compare temperature degrees and air flow rates measures with indoor environmental quality standard to address mitigation ability of this case. The simulation has shown the positive effect of domed and vaulted roofs, and the negative effect of window and wall shading absence. The study results on the ability of case study to mitigate with desert climatic conditions at three levels; ground floor and north-oriented spaces are able to reach IEQ standers and west-oriented spaces need more protection from direct radiations. The study recommended using digital simulation in early design stage to get accurate predictions of building performance.