Abstract: The plateau structure in current negative resistance region has been experimentally observed in strained GaAs/AlAs/InGaAs resonant tunneling diode（RTD）.This phenomenon arises from the coupling between the subbands of emitter quantum well and main quantum well.Their coupling is suppressed by external perpendicular magnetic field.At a certain magnetic field,the plateau structure disappeared.In addition,peak current,i.e.peak-valley-current ratio decreases with magnetic field and the peak voltage increases correspondingly.