The condition parameter evaluation of straddle-type monorail beam based on finite element model modification is a high-dimensional parameter optimization problem, which tends to fall into local optimization. The whale optimization algorithm has the advantages of few required parameters, and good optimization search, while it has rarely been applied in the bridge engineering field, and its applicability needs further verification. Therefore, an analytical framework based on the adaptive whale optimization algorithm and deflection influence line is constructed using finite element model modification techniques, and its feasibility is verified for high-dimensional parametric state assessment of straddle-type monorails. The results show that the adaptive whale optimization algorithm can be used in the condition assessment of straddle-type with a maximum error of 3.5% in the identification of high-dimensional (20-dimensional) parameters, and the accuracy and rate of the algorithm are optimized for the standard whale optimization algorithm; in addition, using the deflection influence line of 1/4 span, mid-span and 3/4 span as the optimization target can reduce the error and improve the accuracy of the condition assessment of rail beams.