A novel Mach-Zehnder interferometer (MZI) structure combined with multi-mode interference is proposed and applied to vibration detection. Different from the traditional MZI which was based on the cascade of two 3-dB single-mode optical coupler (OC), the MZI was composed of multi-mode OC and single-mode OC. A 3dB multimode OC with the coupling ratio of 1∶1 was fabricated using the step index multimode fiber with a core diameter of 105μm and the graded index multimode fiber with a core diameter of 62.5μm, and the MZI was constructed with the multimode OC and another 3dB single-mode OC respectively. For comparison, two single-mode OCs were also used to construct the MZI. Vibration was applied to an interference arm of the MZIs constructed with different types of OCs, and data acquisition and analysis were carried out by an oscilloscope. The results show that the MZI based on a step index multimode coupler with a core diameter of 105μm has the largest detectable vibration frequency range of 1~20kHz, and has the best performance in vibration frequency deviation and vibration frequency discrimination ability.