建立了有阻尼项的摆方程 ,在小信号情况下 ,对方程进行了迭代求解 .由解得的结果得到了增益函数的表达式 .特别对弱阻尼和过阻尼情况进行了计算 ,分别得到了相应的增益函数简化公式 .对阻尼项的来源和物理意义进行了详细的讨论 The pendulum equation with damping is established, and the equation is solved iteratively in the case of small signal. The expression of the gain function is obtained from the result obtained. Especially for the cases of weak damping and over damping, the equations Corresponding simplified function of gain function. The origin and physical meaning of damping terms are discussed in detail