To gain dynamic equation of trolley-load system for overhead traveling crane,the paper performs dynamic analysis of the system and deduces transferring function between the force applied to trolley and load's swing angle from dynamic equation.It comes to a conclusion that load swing reducing force control can be used as effective compensation measure of active anti-swing.Dynamic simulation results show that the optimal evacuation time of the force applied to trolley is a key parameter that has an significant effect upon load swing reducing.