This paper presents a monolithic triaxial micro-opto-electromechanical systems (MOEMS) accelerometer utilizing the Talbot effect of micro-nano gratings, which integrates in-plane and out-of-plane sensing structures on a single chip to enable fully triaxial acceleration detection. Based on optical near-field diffraction, the design achieves high sensitivity, wide linear operating range, and superior acceleration resolution. A theoretical model utilizing the Talbot effect for triaxial acceleration sensing is rigorously established, and active optical power stabilization is integrated to mitigate intensity-induced drift caused by light source fluctuations. Through co-optimization of the mechanical structure and nano-grating parameters, the scale factor of the accelerometer is significantly enhanced. The working principle was validated through both simulation and experiment, with good agreement between theoretical predictions and experimental results. The fabricated MOEMS accelerometer, with a compact footprint of 16 mm×16 mm×0.4 mm, exhibits a sensitivity of 2.9 V·g^-1 (non-linearity <0.68%) and a resolution of 345 μg. The out-of-plane and in-plane accelerometers achieve bias instability below 54.2 μg and velocity random walk (VRW) below 38.7 μg·Hz^-1/2, respectively. These results demonstrate the potential of the proposed architecture for high-precision triaxial inertial sensing in applications such as autonomous navigation, automotive industry monitoring, and industrial machinery condition assessment.