For structural application, composite parts structure is much more affected by load cases than steel part structure. Engine room bracket of EV, which is structural part and is used to bear Motor Controller, Charger and so on, has different load cases for different EV. Three commonest load cases that are Case 1: bearing 65kg (without suspension part), Case 2: bearing 68kg（including 3.5kg suspension part） and Case 3: bearing 70.1kg (including 5.6kg suspension part). According to topology optimization, structurel 1 was obtained, and then CAE analysis including (strength, stiffness and model) was carried out for abovement three load cases. For Case 1 and Case 2, the analysis result can meet the requirement. However, for Case 3, the stiffness and model analysis result can not satisfy the requirement. To meet the analysis result of Case 3, Structure 1 was optimized and structure 2 was obtained. The CAE analysis was conducted and the results can satisfy the requirements. Finally, the vibration durability test was carried out for structural 1 under the three load cases and for structural 2 under Case 3 to prove the structure design and CAE analysis . For structural I, there was no cracks and fracture was confirmd after test of Case 1 and Case 2, but there were cracks or fracture on five positions after test of Case 3. For structural 2, there was on cracks or fracture after test 3. This report discusses the effect of load cases on the structure of the engine room bracket, and the proper structure for different load case was found out by CAE and tests.