Abstract: In this paper, transition timed Petri nets with twophase firing semantics under the week firing rule(or WTTPN's for short) are presented, and they are more suitable for modeling and analysis of conflict structures than the Ramchandani's transition timed Petri Nets with two-phase firing semantics(or TTPN's for short). Paralleling to PN, the framework for formal description and analysis of WTTPN is established, based on which WTTPN's qualitative analysis can be carried out. The relationship between WTTPN and its underlying net is discussed, and it is proved that the WTTPN is equivalent to its underlying net about liveness, boundedness(safeness) and reversibility.