The invention discloses an optical micro-mechanic acceleration transducer and a method based on optical fiber multiple-mode interference effect. In the invention, the transducer is formed by welding single mode fibers, multimode fibers and single mode fibers sequentially, and uses the optical fiber multimode interference effect to realize sensing by changing the lengths, the diameters and the reflective indexes of the multimode fibers; when broad spectrum light of a broad spectrum light source enters to the multimode fibers from the single mode fibers, high-order modes are excited and are mutually interfered; as different modes have different coupling coefficients, the maximum wavelength of light intensity is changed along with the multimode fibers with different lengths during coupling output; the output spectrum of the single mode fiber is detected by a spectrum instrument and then is input to a computer, and the speed of external axial acceleration sensitive to a moveable mass block is sensed according to the change of the light spectrum. The invention improves the measurement accuracy and stability of the optical micro-mechanics acceleration transducer and increases dynamic measurement range.