Multiform simulations of 4 specimens compatibility torsion experiments of a spandrel beam in a longspan prestressed concredt (P.C.) secondary beams floor system are introduced. The results of different simulation methods, such as crack loading, ultimate loading, the torque, twist and torsional stiffness of spandrel beams, are compared and analyzed. The main conclusions are as follows: The compatibility torque of a spandrel beam continuously increases with the load in all the process; The torque does not decrease obviously after cracking; The cracking torque value given by the American Concrete Institute (ACI) Code 31805 is much smaller than the ultimate torque; The reduction parameter of the torsion stiffness in a spandrel beam after cracking equals 0.05~0.10 for a longspan P.C. secondary beams floor system without monolithic slabs, and 0.10~0.40 with monolithic slabs.