Freeze thaw cycle test for rubber modified asphalt mixture was conducted under the condition of deicing salt, then its void ratio, splitting strength and Marshall modulus were determined. The influences of freezing temperature, deicing salt concentration and number of freeze thaw cycles on the void ratio, splitting strength and Marshall modulus were investigated, at the same time the degradation mechanism of mixture after freeze thaw cycle was analyzed by observing its microstructure under the deicing salt conditions. The results show that freezing temperature, deicing salt concentration and number of freeze thaw cycles would produce a greater influence on the void ratio, splitting strength and Marshall modulus of rubber modified asphalt mixture. The key reason for the decline of water stability of mixture is the damage of deicing salt grain on the cohesiveness of asphalt and the expansion and ablation of ice mixture inside.