A new graphical user-defined modeling（UDM） in dynamic simulation of the dispatcher training simulator（DTS） is put forward. Its basic principle and realization flow are discussed. The UDM is realized in dynamic simulation using simultaneous equations，so it can improve the precision of dynamic simulation while facilitating use by the dispatcher. The speed of dynamic simulation can be improved by using the real-time database. The simulation results in Hainan power grid show that the precision and speed are satisfying.