Abstract: The present disclosure discloses a tool wear monitoring method and system under variable operational conditions based on the decoupling of cutting force component. Spindle vibration data of a machine tool is acquired, a data set with labeled tool name information is established according to the machine internal data, a cutting force acting on the tool is estimated in real time based on a vibration signal, and the actual cutting force increased due to tool wear and the maximum allowable theoretical cutting force increased due to tool wear under the surface roughness constraint are calculated. The present disclosure enables tool wear monitoring under variable loads to determine in real time whether the excessive wear occurs based on the part accuracy constraint, and can maximize the service life of the tool.