For the requirements of cantilever vibration characteristics, a vibration system extra points measurement method based on self-mixing interference is purposed. This method is relatively simple, effective, and low cost compared to traditional measurement methods. Starting from the Lang-Kobayashi rate equation, vibration system extra points model is deduced and Monte Carlo random simulation method is used to simplify and correct the half-cycle extreme points formulcs. The order of the cantilever vibration natural frequency is 10 and amplitudes of the characteristic parameters are A10=B10=5.4601×10-13 in the case of free vibration.