The rapid freeze thaw tests and the compression tests were carried out to lightweight aggregate concrete(LWAC) mixed with plastic steel fiber．The variation rule of relative dynamic modulus, mass loss rate and cube compressive strength were analyzed after various cycles of freeze thaw．The relative dynamic elastic modulus and compressive strength of the LWAC were selected as the damage variable， and freeze thaw damage constitutive model was established containing a parameter of plastic steel fiber mass fraction．The results show that plastic steel fiber can restrain freeze thaw damage of the LWAC effectively. The LWAC mixed with plastic steel fiber of 6kg/m3 has the best frost resistance, the longest life and the highest compressive strength. The compressive strength damage model of the LWAC should adopt exponential function model, all of them have higher fitting precision for the freeze thaw damage model of relative dynamic elastic modulus and exponential function model, they all can reflect the change rules of freeze thaw damage of LWAC mixed with plastic steel fiber．