Abstract: Surface failure is correlative to the material performance of structure layer,and strength decay attenuation law of the anti-shear,anti-cracks,anti-fatigue and resistance Moisture Damage are researched based on decay mechanism of the materials,and the relation model of strength decline and its Distribution Pensity Function is established.At the same time,the model is amended by the failure level and surface damage index.So the pavement can be evaluated by the reliability level that represent the structure strength attenuation law.It shows that the shear,cracks,fatigue and moisture damage occurr on the pavement when the reliability level of anti-shear,anti-cracks are all less than 0.85,or anti-fatigue,resistance of moisture damage are all less than 0.75.Otherwise,if waterproof treatment should be implemented in time when reliability level of resistance moisture damage is more than 0.65,the begining time of large and medium pavement maintenance can be delayed for 30%.