The current boom in Micro-electromechanical Systems combined with the advent of the physical reservoir computing make it possible to break through the bottleneck of traditional sensing paradigms based on physically separated sensors and processors. Here, we report a pioneering work on a novel sensing paradigm of analog-to-feature using a stiffness modulated micromechanical resonant accelerometer. Specifically, the amplitude-acceleration nonlinearity of the accelerometer and its transient nonlinearity serve as the nonlinear dynamics of our physical reservoir computing to categorize the accelerometer input. Furthermore, we perform ten times tenfold cross-validation tests and use the confusion matrix to test its classification performance on a data set of the different acceleration corresponding to the different motion postures generated by a six-axis IMU. The results show a classification accuracy of 97.33%, which proves that our MEMS accelerometer-integrated reservoir computing enables data processing ability locally at the sensing side for efficient distributed processing.