In order to decrease the manufacture cost of all-terrain vehicles rapidly and effectively,a finite element model for the frame structure of all-terrain vehicles is built by using pre-processing software HyperMesh. The correctness of the model is verified by computing the freedom mode of all-terrain vehicles with Optisturct solver and contrasting it with existing test results. Through applying Optistruct solver and Fatigue to analyze stress distribution,deform and fatigue life of the frame under multi-conditions,and combining with sensitivity analysis results,the lightweight project of the frame is put forward. The validity of this lightweight project is identified after analyzing the optimized frame structure intensity and the fatigue life. The lightweight result show that the frame structure is lightened 6.6063 kg. At the same time,it shows that the structure optimization efficiency and the lightweight effect are enhanced by sensitivity analysis.