The enforcement process and theoretical background of the forced uncoupling method, together with its meanings of mathematics and physics, are analyzed by introducing complex mode superposition formula for calculating seismic responses of non-classically damped linear system. 从非比例阻尼弹性结构地震反应复振型分解法的解析表达式出发,对强迫解耦法的实施过程、理论背景、数学近似和物理意义进行了分析;