The site occupancies and antisite defects play important role in the physical and mechanical properties of intermetallic compound alloys. In this paper, the effects of Al concentration (c_Al) and temperature (T) on the change trend of site occupancies and antisite defects in B2-FeAl, which has attractive properties, are investigated by phase field method. The numerical results show that the increase of c_Al or the decrease of T can result in an acceleration of solute atoms segregation in matrix phase, and make site occupancies of Al and Fe as well as antisite Fe/Al reach equilibrium state earlier. Meanwhile, the increase of c_Al or the decrease of T can enhance the site occupancies of Fe and Al and reduce the two types of antisite defects. Furthermore, the theoretical results show that the change of c_Al and T is not able to change the main type of antisite defect in B2-FeAl ordered phase.