Polyurethane is a kind of elastomer material with the advantages of light weight, high elasticity, wear resistance, corrosion resistance, etc. It is widely used in transportation, construction, machinery parts, national defense military, etc. It will be subjected to fatigue damage by the action of tensile load in many conditions, which will reduce the service life of the components and may cause big accidents. Therefore, it is necessary to study the fatigue damage characteristics of polyurethane components. In this paper, molecular dynamics simulation is used for the first time to study the stress-strain characteristics and microscopic evolution of different tensile strain rates under loading. The results show that the reduction of strain rate makes the material produce an initial crack location from the tensile end to the fixed end of the vicinity of the fracture location for the tensile end of the maximum stress with the reduction of the tensile rate decreases, the internal molecular chain slip fracture under stretching leads to cracking and tensile fracture of the material.