Vortex-induced motion (VIM) of an offshore platform with multi-columns is an area of sig-nificant focus in the field ocean engineering. VIM involves the complex fluid-structure interaction problem. In this paper, the Reynolds-averaged Navier-Stokes solver combined with the shear-stress transport k-ω turbulence model for the Navier-Stokes equations was used to simulate the VIM of multi-columns with low mass ratio for different flow-approaching angles and reduced velocities. The values of natural period and dimensionless damping coefficient for columns were taken from the model test in the State Key Laboratory of Ocean Engineering of Shanghai Jiaotong University. A com-putational grid was set up using GAMBIT software. The coupling fluid-structure interaction between the columns and the flow field was obtained by calculating the instantaneous lift and drag forces acting on the multi-columns caused by the external flow field. The differential motion equation was solved by fourth-order Runge-Kutta method, which was manually written into the user-defined func-tions, and dynamic mesh technology was then adopted to update flow field. The maximum and nomi-nal statistics methods were used to analyze the amplitude of VIM. When the reduced velocities were small, the ‘jump’ phenomenon was observed in the amplitude curve for 0° flow-approaching angle regardless of whether motion in the stream-wise direction was limited. The maximum amplitude was 0.5D when motion in the stream-wise direction was not limited and was slightly smaller than the maxi-mum amplitude of the limited motion in the stream-wise direction 0.57D). The restriction of motion in the stream-wise direction and the selection of statistical method significantly affected the size of the ‘lock-in’ region. Galloping at the low-frequency and multiple-frequency lock in phenomena was observed for the flow-approaching angles of 0° and 45°. Variation trends of equilibrium position with reduced velocity were very close for the three typical flow-approaching angles. When the re-duced velocity was greater than 6.0, the maximum stream-wise amplitude heading was 22.5°, where-as the minimum stream-wise amplitude heading was 0° heading. The vortex shedding pattern of mul-ti-columns showed the 2P mode.%多立柱海洋平台的涡激运动是非常复杂的流固耦合问题也是近年来海洋工程领域的研究热点。文章引入雷诺平均法求解NS方程、结合SST k-ω湍流模型采用耦合算法对低质量比多立柱在不同流向及流速下的涡激运动进行了数值研究，立柱运动固有周期及无因次阻尼系数取自上海交通大学海洋工程国家重点实验室的相关实验数据。采用分区法建立了计算网格，多立柱和流场的流固耦合通过计算外部流场作用于柱体的瞬时升力和拖曳力，将求解运动微分方程的四阶Runge-Kutta代码嵌入UDF求解器中，运用动网格技术实现流场更新并采用最大值统计法和标称统计法对涡激运动振幅幅值进行统计，研究发现：0°流向较小约化速度时，无论限制流向是否，振幅都存在跳跃现象，不限制流向下横向最大振幅为0.50 D，略小于限制流向的0.57 D，较大约化速度时，横向振幅出现了锁定现象，但是否限制流向和统计方法的选取对锁定区间长短有所影响，0°及45°流向时候观测到了低频驰振及多频短暂锁定现象，三个典型流向下流向平衡位置随流速的变化趋势基本相近。不限制流向下约化速度大于6.0时，采用标称统计法得到的22.5°流向横向振幅最大，0°流向最小，多立柱尾涡结构形式表现为2P模式。
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