Abstarct: We study in this research the Evaluation of Behavior Factor For Combined EBF And CBF Steel Structure. In the almost time the structure engineers inevitable to use combined EBF and CBF bracing system in structure because they want to contour better architect plan for have opening in the bracing system. when we use the combined EBF and CBF bracing system in structure we don’t know about the behavior factor of this combined bracing system because the earthquake regulation of Iran don’t offer any number to behavior factor of this system. We start this research to offer the solution for this system and we proffer the new system of bracing that we called it MBF bracing system. The result of this research is : if we use combined EBF and CBF bracing system in structure for the structure under than the 8 story when the proportion number of EBF divided by number of CBF elder than 3 and eccentricity of EBF lixnk beam under than 0.3 ( ≤ 0.3 ) then you can use the behavior factor of EBF bracing system for design structure else you must be use behavior factor of CBF bracing system for design structure. The proffering MBF bracing system can absorb energy of earthquake more than EBF bracing system and CBF bracing system and when the earthquake pass the building there is not plastic hinge in the columns and beams then if we change the MBF bracing the structure is ready for next earthquake.