Abstract: For the cracking problem taking place in the surrounding area of the floor suspension longitudinal beam of a non-loaded off-road vehicle prototype during the reliability test at the Dingyuan test field in Anhui province, some analysis and verification studies were carried out with CAE and road tests. Considering the determined cracking causes of the surrounding area on the floor longitudinal beam, an improvement plan was proposed for optimal structure design. Through the CAE analysis and comparison before and after the structure improvement, the structure optimization plan was verified in practical prototype reliability test.