FLNG ( Floating Liquefied Natural Gas ) is a new type of offshore floating LNG production system, and FLNG cryogenic flexible pipeline is the key equipment to realize LNG transportation.  As a structural layer directly contacting with LNG in FLNG cryogenic flexible pipeline, metal bellows largely determines the overall mechanical properties and safety performance of cryogenic pipeline.  In this paper, the wave diameter R and the ring plate length L of the basic structural parameters of the bellows are innovatively used for the sensitivity analysis of the mechanical properties of the bellows in the ultra-low temperature environment, so as to solve the problem that the wave height will be changed in the previous sensitivity analysis of the bellows, making the sensitivity analysis more direct and correct.  After sensitivity analysis, the sample set of structural parameters on mechanical properties is established based on the data of sensitivity analysis, and the RBF surrogate model is constructed by the sample set. The error analysis between the predicted value of the surrogate model and the specification and the sample set is carried out to verify the accuracy of the numerical analysis and the surrogate model.  Finally, the multi-objective optimization is carried out according to the genetic algorithm and RBF surrogate model, and the Pareto optimal solution is obtained with the maximum tensile stiffness and the minimum bending stiffness as the objectives and considering the process constraints, which provides a reference for the design of bellows considering the practical engineering application.