Abstarct: Structural discipline is one of the most important parameters affecting seismic behavior, which should be created by appropriate interaction between architectural and structural engineers in the building. Investigating the behavior of structures in past earthquakes, it can be seen that the existence of structural order in lateral bearing system has strongly influenced the seismic behavior of the structure. These observations show that buildings that have an asymmetrical lateral bearing system due to their particular architecture are a lot of damage during the earthquake. On the other hand if the afterearthquake occurs after the main mainshock, it will increase the amount of the damaged and disrupt the structure's performence. In this study, the fragility curves for a three , five and eight-story structure with a steel moment resisting frxame system with a torsional irregularity in the plan under the influence of earthquake and after shock have been investigated. The structure is designed according to rules of Iranian Regulations and after the finalization of the sections , the structure is modeled in 3D software (OpenSees). Then, by selecting a number of appropriate accelerations and adapting to the conditions of the region, the nonlinear increases dynamic analysis (IDA) will be obtained, and the maximum dirift of floors is calculated as the demand parameter; By selecting the relative displacement capacity of the four seismic performance levels, minor, moderate, extensive, and complete damage according to the American Hazus Code, and using structural trust relationships, the seismic fragility curves of this system for four different damage levels It is obtained and discussed the results of torsional irregularities and effect of aftershock in the seismic fracture of the building.