The invention discloses a rotor vibration protection method based on harmonic component decomposition. Shaft vibration data from a front bearing bush and a rear bearing bush on the same rotor are acquired, and subjected to harmonic component decomposition to obtain X-direction and Y-direction rotor first-order vibration in-phase components; vibration conditions of the rotor are determined through variation and comparison of such data, and then a determination can be made on whether trip protection is carried out. Compared with the prior art, the rotor vibration protection method based on harmonic component decomposition has the following advantages: monitoring the vibration of the entire rotor can be achieved through analysis of the vibration data from the bearing bushes for a front shaft and a rear shaft; moreover, with sectionalized protection set up for shaft vibration values, and protection maloperation caused by single-point protection is avoided, and the case of falsely triggered trip can be effectively avoided; according to tracking of values within normal periods of time, a reference base can be updated in real time and abnormal conditions of rotor vibration can be determined rapidly, and accordingly, a determination can be made on whether trip is triggered. In such a way, the case that protection is influenced by frequent trip of the unit that is oversensitive due to interference of background vibration in some situations is avoided.