The control functions can be easily formulated in many various ways, leading to the input function that can be treated as a disturbance or as a control signal. It is also possible to generate the equations of state in relation to the defined inputs and outputs of the system. During the analysis process, by using all acquired data, GRAFSIM software generates operating dynamical characteristics (transmittance), and matrices of the state that describe the model of a mechanical system. The GRAFSIM software in the automated way designates equivalent transmittance of the analysed system on the grounds of the block diagram’s set inputs and outputs, and determines the matrices of the state. The method of determining operating dynamical characteristics in GRAFSIM is directly based on designating equivalent transmittance of the system in view of its defined input and output (simplification of the block diagram). The software that was shown and discussed in the article constitutes a cheap and user-friendly tool for the engineers making analysis of the vibrations of complex 2D and 3D mechanical systems