The ratio of every coefficient of nonlinear stiffness terms to coefficient of linear stiffness term at different horizontal tension levels was analysed for the first three vibration modes of an iced conductor.Through discussing the relationship among amplitude of vibration,horizontal tension,linear restoring force and nonlinear restoring force,the main factors influencing strong or weak geometric nonlinearity of an icied conductor system were determined.On this basis,the steady state amplitudes and vibration frequency of the system were calculated with the undetermined natural frequency method.Numerical results showed that the amplitudes of its vibration modes increase with increase in wind velocity;natural frequency of each vibration mode is far from its initial value when the system is subjected to the effect of strong geometric nonlinearity.The analysis results with the conventional normal form theory were difficult to meet the accuracy requirements of model analysis,but the analysis results here could grasp the vibration characteristics of the model of an iced conductor system well.%分析了覆冰导线前三阶模态中在不同水平张力下各非线性刚度项系数与线性刚度项系数的比，通过讨论水平张力，线性恢复力、非线性恢复力与振动幅值之间的关系，确定了影响覆冰导线系统几何非线性强弱的主要因素。在此基础上，应用待定固有频率法计算了系统的稳态幅值和振动频率。数值模拟表明：各模态幅值均随风速增大而增大，且当受到强几何非线性因素的影响时，各阶模态的振动频率将远离初始频率，此时传统规范形理论的分析结果难以满足模型分析的精度要求，而该研究结果则可以对模型的振动特性有比较准确地把握。
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