Abstract: Gear vibration signals are cyclostationary. Character cyclic frequencies of its spectral correlation density (SCD) function are harmonic clusters, whose basic frequencies traverse modulation frequencies and meshing frequencies of the system. Therefore, the information of the SCD for harmonic cyclic frequency clusters

is concentrated as accumulation energy factor (AEF) for gear precise condition monitoring in this paper, which named as meshing vibration monitoring factor and modulation monitoring factor separately. AEF can be employed to monitor certain vibration phenomena in gear transmission system, which is favorable for fault location determination. AEF extracts information from whole analysis frequency band, and it is superior at early weak fault identification. Experimental results in this paper verified the sensitivity and the practicability of AEF.