Quantum noise is one of the main noises affecting the laser interferometric gravitational wave detection. To cope with quantum noise and further improve detection sensitivity, this paper applies the quantum transfer function method to rederive the source attribution of quantum noise in conventional Michelson interferometers. The findings reveal that for two types of quantum noise-radiation pressure noise and shot noise-radiation pressure noise can be directly attributed to the amplitude quadrature fluctuations of vacuum fluctuations at the unused port of the interferometer, while shot noise can be completely attributed to the phase quadrature fluctuations at the unused port only under certain conditions. Provided that the source attribution of the quantum noise is clearly known, the squeezed light technique can improve the sensitivity of detectors. However, when adopting unequal arm interference detection schemes, attention must be paid to the length difference between the two unequal arm lengths.