To the impact which mixed-use to the fire risk, this issue considers a perspective of system dynamics that emphasis the intern structure of a system and the casual-effect relationships between variables as an analytical approach. In practice, it refers to modal-construction process of system dynamics mainly. Only commercial and residential use were blend in landuse that in the discussion. In the phase of intern variables identifying, important components were searched from fire science literatures. Fatal vulnerable factors were collected from case studies or reports the other way. The casual-effect loops were sketched; and translated to numerous equations. The research region is chosen the blocks had significant mix-use effect in Tamsui Town, Taipei County. The modal was repeated improving by referencing mainly the casualty and number of fire cases during 2000 to 2006. In conclusion, the modal not generally displays expectational outcomes that two strategies increasing the rate of the installation of spray system and fire insurance but also shows the impact given by strategies. With difference between simulated outcomes and real statistics, it has the ability of suggesting critical variables ignored at first.