After analysing the armature force of the relay, the author directly obtains the expression for parameter analysis of the general-purpose hysteresis loop in the relay using alternating and direct current, and therefore reveals the forming mechanism of the hysteresis loop. 本文通过对继电器的衔铁受力分析,直接得到了交直流继电器通用的滞环参数解析表达式,从而揭示了滞环形成机理。