The sensing technology based on laser speckle has become one of research hotspots in the field of optical sensing to measure the stress, vibration, distance, speed and flow rate, owing to its significant advantages in simplicity and high precision. A set of stress sensing system based on laser speckle was designed in this paper. The wavelength of 405 nm laser was used as the light source in the system. The voice coil motor was used to vibrate multimode fiber, and CCD image sensor acquisition system was applied to image for polishing glass surface. MATLAB software was used to analyze the collected speckle images, calculating the contrast, fitting the curve of the speckle contrast. The results show that speckle contrast changes reflect the stress variation in the multimode fiber. Through the multimode fiber stress changes can be judged whether there is an intruder, anti-theft function is realized.