In this paper a new idea for beam-pbunching in RFA was proposed. Without any applied RF power source, beam pbunching can be carried out. The bunching device is the same as the conventional pbuncher in structure, but obeys the conditions as follows:(1)a considerable detuning between the repetition of the beam bunch and the characteristic frequency of the cavity; (2) the characteristic frequency of the cavity is higher; (3) resistivity of the material of cavity is higher. A set of experimental check was performed on the corresponding equipment built in CIAE. A proper bunching was observed.