Forest fire spread risk (buildings) refers to the possibility of forest fire spreading and causing damage and loss to buildings. It can identify areas where forest fire is prone to spread and cause serious damage and loss to buildings. Scientific assessment of forest fire spread risk (buildings) can provide scientific basis for accurate prevention and control of forest fires, and can bring important theoretical and application value. The mountainous districts of Beijing (Fangshan, Mentougou, Changping, Yanqing, Huairou, Miyun, Pinggu) were used as the research object. The multi-scale forest fire spread risk (buildings) assessment in the mountainous districts of Beijing was carried out based on the risk assessment framework of "hazard-exposure-vulnerability". The subjective and objective weighting method of AHP and entropy weight method were used to determine the index weight, and the weighted comprehensive evaluation method and the area weighted average method were used to calculate the multi-scale forest fire spread risk (buildings) index. The natural breakpoint grading method was used to classify levels, and the spatial autocorrelation analysis method was used to explore the spatial correlation pattern of the forest fire spread risk (buildings) index. The research results show that: (1) The comprehensive weight of building exposure reaches 0.5123, which is the main factor affecting the forest fire spread risk (buildings). (2) The assessment results of forest fire spread risk (buildings) in Beijing Mountainous District showed that the high risk areas accounted for 3.82%, 13.30%, and 17.95% at the subcompartment, township, and district scales, respectively. (3) The spatial heterogeneity of forest fire spread risk (buildings) index at the subcompartment scale in the mountainous districts of Beijing was significant, showing the law of agglomeration distribution, with 16,641 HH (high-high) cluster subcompartments. The results showed that the high-risk subcompartments of forest fire spread risk (buildings) were mainly Platycladus orientalis, Pinus tabuliformis and shrubbery in the mountainous districts of Beijing. It is suggested to strengthen the forest fuel management in the built-up areas and the border areas between the field and the city.