Background: Crop straw is a valuable renewable biological resource. In this study, a mobile straw granulator was designed to fully and efficiently use crop straw. The key crushing mechanism device of the mobile straw granulator was also designed in detail. Methods: The first three natural frequencies and vibration modes of the crushing roller are obtained by applying ANSYSWorkbench software to the modal analysis of the crushing roller. Results: The lowest natural frequency of the crushing roller was 165.83 Hz, which was higher than its working frequency of 30 Hz and would not cause resonance. Three factors and three levels were tested using the average resistance of the blade as an index and the blade edge angle, the blade thickness, and the blade end width as the test factors. Conclusion: The optimal parameter combination obtained by software analysis is blade edge angle of 30°, blade thickness of 8 mm, and blade width of 75 mm. With this parameter combination, the blade power consumption is the smallest, the service life is the largest, and the crushing effect is the best.