In this paper, we propose a novel scheme of measuring a coupled but uneasy detected vibration mode through surveying another much easier detected vibration mode in a complex mechanical system. Through measuring the frequency dependence of phase lag of strain behind stress, i.e., the apparent mechanical dissipation-frequency spectrum, for the easy detected vibration mode, we are able to obtain the corresponding resonant absorption peak for the coupled vibration mode in addition to the expected main system resonance. By studying the observed resonant absorption peak: peak position, peak width and peak height, we can obtain the detailed information about the coupled vibration mode: the intrinsic resonant frequency, dissipation and coupling coefficient. Through measuring the apparent mechanical dissipation frequency spectrum of torsion vibration, the detection of the progression vibration about the pendulum axis is presented as a representative example of our scheme.