Abstract: Liquid metal reactor (LMR), with the great advantages of high safety and good economic benefits, has obvious advantages and broad application prospects in the fourth generation nuclear power systems. Helical coil steam generator is one of the most important equipment for liquid metal reactors which have compact structure and high heat transfer efficiency. Natural frequency of tube bundle is an important parameter in flow induced vibration (FIV) analysis. In this paper, the natural frequency of helical coil steam generator tube bundle was studied. Based on simplifying constraints at both ends of the heat transfer tubes to simple support, the computational fluid dynamics (CFD) simulation was carried out to reveal the effect mechanism of helix angle β, number of supports S and coil radius R, on natural frequency of heat transfer tubes in air. The relative error between the CFD simulation results and experimental values is within 5%. Considering the accuracy of actual processing and manufacturing, the numerical simulation settings have great engineering practicability. The result shows that the increase of β- and R will induce the reduction in natural frequency, and the increase of S will lead to the adverse result. Therefore, we can improve the stability of the heat transfer tubes by increasing β and S or reducing R. Based on CFX simulation calculation, the influence mechanism of tube bundle structure parameters on the natural frequency of heat transfer tubes in liquid metal environment was studied. The increase of layer pitch ratio a, the same layer pitch ratio b, will lead to the increase of natural frequency, and the increase of β will lead to the adverse result. The natural frequencies of heat transfer tubes in liquid metal environment were obtained, and the interaction table was established based on orthogonal experimental design to investigate the effect of the three structural parameters layer pitch ratio a, the same layer pitch ratio b and the helix angle β, on the added mass coefficient. The results of orthogonal analysis show that a and b have a great influence on the added mass coefficient CM1 in the out-of-plane direction and the added mass coefficient CM2 in the in-plane direction of the helical coil tube, respectively. And the effect of β and the coupling effect between various factors can be ignored. Then, the added mass coefficient curve was drawn. This research provides data reference for the prediction of natural frequency of heat transfer tubes and the study of FIV of tube bundles, which are of great importance for avoiding the failure of heat transfer tubes.