This paper studied a beltdrive system containing a translating belt, two pulleys, accessory systems, and a oneway clutch. The driven pulley and the accessory system were coupled by the oneway clutch. Moreover, the transverse vibration of the translating belt was taken into account. Therefore, the derived coupled discretecontinuous nonlinear equations consist of integropartialdifferential equations and piecewise ordinary differential equations. The continuous nonlinear equations were truncated to a set of nonlinear ordinary differential equations by using the Galerkin method. The steadystate responses of the coupled vibration of the beltdrive system were investigated by the numerical harmonic balance method. Moreover, the effects of the oneway clutch on the power system were studied by comparing the frequencyresponse curve of the translating belt with and without oneway clutch device. The nonlinear dynamic characteristics of the beltdrive system were studied. Furthermore, the steadystate responses of the beltdrive system were investigated at the higher excitation frequency for the first time. In addition, the steadystate responses based on the harmonic balance method were confirmed by the RungeKutta algorithm.