The retractable spray boom is one of the key components in a plant protection machine, which is assembled from beams of different length held together with bolting. In order to determine the dynamic characteristics of the bolted boom in a plant protection machine, the reduced order model of the bolted boom with a four-parameter Iwan model was established and confirmed by experiments. Based on the static and dynamic characteristics of the bolted boom, it is indicated that the boom with the Iwan element shows a stronger damping and higher frequency. The influence of the system parameters on the amplitude of the steady-state responses in output points was also explored, which shows the interplay among the excitation force, the parameters of the Iwan element and the linear modal damping ratio. The work provides a deeper insight into the more detailed response characteristics of the bolted boom in plant protection machines.