We design and fabricate a novel optical accelerometer based on high-order diffraction beam interference with a built-in phase-generated carrier modulator. A proof-of-concept prototype is tested and achieves a resolution of $96\mathrm{ng}/\surd \mathrm{Hz}$ with a dynamic range of $60\mathrm{g}$ . By employing optical interference between $\pm 1$ order diffraction beams from a grating translating perpendicular to an optical beam for acceleration sensing, the accelerometer realizes a wide dynamic range, while maintaining a high resolution. Compared with prior optical accelerometers, the interference in this structure is free from the effect of short coherence length or beam divergence, and a greater than ordinary dynamic range is obtained. The proposed design is also applicable to a MOEMS platform, offering a new thought in the design of high-performance MOEMS accelerometers.