Under the traditional design scheme, the design quantity of main girder of the bridge erector is redundant and there are many consumables, which will reduce the production efficiency, and the existing optimization methods have the problem of low convergence accuracy. An enhanced beluga whale optimization (EBWO) based on quadratic interpolation strategy was proposed, and lightweight design of main girder of the 600t bridge erector was carried out. Firstly, six test functions were applied to evaluate and compare the effectiveness of the beluga whale optimization (BWO), EBWO and three other prevalent optimization algorithms, focusing on their convergence characteristics. Then, a mechanical analysis was conducted on the bridge erector girder under the real loading conditions. An optimization model was established by combining bridge girder design specifications and mechanical requirements, and the cross-sectional area optimization of main girder of the bridge erector was carried out. The results show that EBWO has the enhanced stability and convergence characteristics. It is proved that the optimized main girder is reduced by 19.3%, and can meet the safety requirements.