The paper studied the noise elimination methods for the signals observed from a self-mixing-laser diode (SM-LD) based sensing system. The core part of the sensing system consists of a LD, a lens and an external vibrating target. The proposed noise elimination methods are applied on both the simulated and experimental sensing signals. The results presented in the paper show the noise contained in the sensing signals can be effectively eliminated. As a consequence, the vibration trace of the target can be reconstructed with high accuracy using this sensing system.