The invention discloses an electromechanical signal based running state evaluation method for tap changer (OLTC). As an important device in a transformer, reliable work of the on-load tap changer (OLTC) has great significance in the transformer as well as the whole power system. The method comprises that original signals including current and vibration signals are collected and extracted; enveloping analysis is carried out on the current signal, singularity and wavelet packet analysis is carried out on the vibration signal, and characteristic quantities including operation time length, impactcurrent, Delta current, singularity index and wavelet packet energy entropy are extracted; and a fuzzy clustering method (FCM) is used to evaluate the mechanical running state of the tap changer basedon the characteristic quantities.