<p>Low-rise buildings are widely distributed in residential areas and small commercial zones. Therefore, ensuring their fire safety is crucial for protecting lives and property. However, existing fire risk assessment methods involve incomplete index systems and do not sufficiently consider risk factors in fire scenes, thereby failing to identify hazards accurately. Consequently, these methods cannot be used to formulate effective fire prevention strategies. Accordingly, this study developed a fire risk assessment model based on extension cloud theory and numerical simulation for low-rise buildings. It established an evaluation index system covering the dimensions of personnel, equipment, management, building, environment, and dynamic risk in fire scenes and then determined index weights by using a combination of the Decision-Making Trial and Evaluation Laboratory and best–worst methods. Dynamic risk factors were simulated using PyroSim to analyze how temperature, CO concentration, and visibility affected risk. The following fire development patterns were identified by comparing five scenes: (1) smoke spreads preferentially to the top floor and the floor on which the fire originates; (2) stairway fires cause vertical smoke movement that endangers upper-floor evacuation; (3) fires in the middle of a corridor cause heat accumulation and thus hinder evacuation from the corresponding floor; (4) a mechanical smoke exhaust system with a reasonable layout reduces fire risk; and (5) automatic sprinkler systems can cool the surroundings, capture smoke, improve visibility, and increase the time available for evacuation. Overall, this study offers new insights and methods for fire risk assessment in low-rise buildings.</p>