The work aims to determine the relationship between vibration and fit clearance of stepper motor driver and EPE cushion foam. The stepper motor drivers were selected as the research product and EPE cushion foam with densities of 20, 28 and 32 kg/m3 were used as vibration isolation packaging. The fit clearance between the product and the EPE cushion foam in the vertical direction was −4, −2, 0, 2 and 4 mm. Customized wooden fixture and EPE cushion foam model with the density of 32 kg/m3 and the fit clearance of −4 mm were used for random vibration test analysis according to the PSD power spectral density curve of American ASTM-D4169. According to the test results, the simulation model, contact, mesh generation, etc. of the corresponding type of package were modified until the simulation results were in good agreement with the RPSD curve of the test results. According to the simulation setting of the package, the series of fit packages with densities of 20 and 28 kg/m3 were simulated and analyzed. For the EPE cushion foam with the same density, the vibration intensity of clearance fit was lower than that of interference fit. The RMS value and vibration intensity were the lowest at 0 mm fit. For the same fit, the lower the EPE cushion foam density was, the smaller the RMS value was and the lower the vibration intensity was at interference fit. The higher the EPE cushion foam density was, the smaller the RMS value was and the lower the vibration intensity was at clearance fit. When EPE cushion foam is used to pack the stepper motor driver, the vibration isolation performance of 0 mm fit is the best and the vibration isolation performance of clearance fit is better than that of interference fit under the same density of EPE cushion foam and level of external excitation.