In this paper, we investigate the regulation of the synchronous firing behavior of leech neurons with inhibitory coupling by time delay and hyperpolarizationactivated cation current Ih. Numerical simulations reveal that time delay, coupling strength, and Ih current can all induce rich synchronous transition behaviors, such as from synchronous period6 bursting to synchronous period1 bursting. By means of ISI bifurcation and fastslow variable dissection method, the dynamic reasons of Ih current induced synchronous transition behavior are obtained. The results show that both time delay and Ih current are important factors affecting the synchronous behavior of leech neurons.