Passive defense is recognized as a key strategy for reducing the vulnerability of urban infrastructures to natural and man-made threats. This research aimed to analyze risk and present a physical organization strategy for the Shahid Mahallati Flower Market in Tehran using a passive defense approach. The present study is applied in terms of purpose and quantitative-descriptive in terms of method. The required data were collected through documentary studies, field observation, and completing specialized checklists. The risk assessment was conducted by combining FEMA risk analysis methods and the RAMCAP framework (the indigenous method of Iran passive defense organization) and based on the three components of threat, vulnerability, and consequence. The statistical population was all critical assets of the complex (including 600 booths, the management building, the control room, and passages). In this study, for the first time, the principles of passive defense in a flower market (as an example of a highly dense commercial-service center) were systematically and quantitatively measured, and risk numbers were calculated for each asset.