The coupling resonance is induced by the plasma electrostatic oscillation in the magnetic trap consisting of the cross-field at the surface of the unbalanced magnetron sputtering target and the potential well composed of the magnetron sputtering target and the opposite bias substrate in parallel. Langmuir probe was used to study the plasma properties and power spectra density (PSD) of the floating potential signals. Under typical discharge conditions, the eigenfrequencies in both traps were respectively in the range of 30—50 kHz or 10—20 kHz, and the electron temperatures in both traps calculated with the acoustic standing wave mode conformed with the experimental results.