Concerning the traffic jams due to bad speed control for cyclic traffic flows, a suppression method was proposed on Washout control. With optimal velocity function, a nonlinear dynamic mathematical model for cyclic traffic flow was derived. To reduce the unreasonable factors of taking drivers' sensitivities as main parameters, Washout control was employed to obtain stability on its equilibrium. Parameters to keep system stability were also considered by using small gain theorem. Simulating a cyclic traffic flow with 20 cars, the simulation results show that the traffic flow reaches its equilibrium in 100 seconds with the proposed controller.