Abstract: There are many specifications and types of nuts that need to be tightened during assembly, due to the great differences in the structure of different types of automobile fuse boxes. Manual assembly requires multiple replacement of electric batches, not only the efficiency is low, but also the tightening torque cannot be accurately controlled. An automatic tightening machine for multi-specification nuts based on torque monitoring is designed, which can automatically achieve the functions of loading, positioning, tightening, tightening torque real-time detection of multi-specification nuts and automatic wrench replacement. The prototype test shows that the system is reliable and the tightening effect is good, the production efficiency is increased by more than 20% compared with manual assembly, and the flexibility of automobile fuse box assembly is improved.