In the method for the measurement of vibration displacement by way of machine vision, the segmentation of the marked image of vibration is the key point in the processing procedure. The segmenting result directly affects the final measurement accuracy. However, the segmenting results of the traditional Otsu threshold segmentation method and the improved algorithms are not satisfactory because of the small number of pixels of the target in the marked image and the interference factors in measurement.In order to get a better segmentation algorithm, this paper firstly explores the problems existing in the improved algorithms of segmenting the marked image under the interference of impulse noise, strong light and shadows. Then, an improved Otsu algorithm is proposed based on the distribution information of the gray level between the threshold and the target peak.Based on the improved algorithms, the ratio of the difference of the gray values between the threshold and the nearest target peak to the population, and the ratio of the sum of the pixel number of thein gray values to the population, are both taken as the weight. Finally, the segmentation experiment of the marked image and the measurement experiment of vibration displacement are carried out under the condition of multiple and complex interference. Experimental results show that, the proposed algorithm is still able to effectively segment the marked image under interference, and the deviation of the target's position is lower than that of other algorithms in general. Meanwhile, the accurate measurement of vibration displacement is realized.