An improved laser Moire deflectometry system is designed for fire safety science research. It has larger scope than conventional system. Relatively larger scale experimental simulation can be carried out with this system. It was used to study the flow procedure of ceiling jet and propagation of fire on solid combustible material. Research of ceiling jet illustrates flow procedures of ceiling jet of different ceiling constructions. The procedure of hot buoyant plum propagating across barrier was clearly displayed. It provides reference to ceiling construction design and dynamic performances evaluation of fire detect system. Detection time lag is one of three distinct time lags that contribute the effectiveness of fire detection systems and fire mitigation strategies. Two sets of photographs are present corresponding to ceiling jet with different cross girders.