Free vibration as well as forced vibration of a dry friction oscillator which was composed of Iwan model and a mass were investigated by harmonic balance method (HBM).For free vibration,the nonlinear equations of the motion of the system in the processes of loading and unloading were presented respectively.Then,based on HBM,the first-order approximate harmonic solution of each equation was derived.A strategy was proposed to detect the moments of zero velocity so as to achieve the correct numerical solutions.The results of a numerical example show that the solutions of HBM coincide well with those of the numerical method,so the validity of the method for such problem is verified.For forced vibration accompanied with microslip,the amplitude-frequency relationship of the system was derived by HBM.Finally,the damping characteristics of the Iwan model were studied.It is seen that a nonlinear relationship exists between the equivalent viscous damping of the model and its displacement amplitude.