Modal analysis mainly studies the dynamic characteristics of the system in the frequency domain. The mode analysis method can determine the characteristics of the main modes of each order of the structure in a susceptible frequency range, which can predict the actual vibration response generated by the structure under the action of various vibration sources in this frequency band. Based on this, this paper first to the single degree of freedom and multiple degrees of freedom mode using MATLAB analysis, and then use the inventor mechanical arm shoulder joint modeling, introduced the mode analysis theory based on Matlab, through the command line input mode and frequency response analysis, obtain the first six modal parameters, and avoid shoulder joint resonance phenomenon in the process of work, determine the scope of safe work. This paper analyzes how to use MATLAB for computational mode analysis to provide reference for related model establishment, optimization design and fault diagnosis.