A perturbation sensor based on the detection of a weakly coupled few-mode multi-core fiber (FM-MCF) specklegram was proposed and experimentally demonstrated. The sensor has a cascaded fiber structure consisting of a “single mode fiber-multi-mode fiber (MMF)-multi-core low-mode fiber." After the light field of a single-mode laser passes through the MMF, all seven cores in the FM-MCF can be illuminated, and an image with seven sub-specklegrams can be received by a camera at the end of the FM-MCF. In an experiment, perturbation was applied to different positions of the FM-MCF and specklegrams were collected at the same time. Based on the strong-coupling characteristic of the core and weak coupling between the core, the fiber structure achieved a high precision classification of 99.46% for 15 disturbance locations, with a spatial resolution of 3 cm, which was much higher than the results for disturbance locations when using only MMF specklegram detection. The capability of the sensor to detect the perturbation position and intensity simultaneously was also tested, and the recognition accuracy was close to 100%. The experimental results showed that the proposed sensor has the advantages of low cost, a simple structure, easy demodulation, and high precision.