Abstract: To solve the problems revealed from the process of the production, calculation by hand and computer was conducted to find out that when the threaded fasteners are tightened according to the requirements of the national standard i.e., the standard of “Safe Technical Requirements For Agricultural Machinery Operating(Grain Combine)” and machinery industry standard “Product Quality Classification of Grain Combine”, insufficient bolt intensity has happened. It indicates that the value of tightening torque of threaded fasteners fixed by these two standards is higher than normal. It was pointed out that the value of tightening torque of threaded fasteners has nothing to do with nominal diameter and quality class of bolt stock. It should be guaranted that all parts of the engine can work normally, reliably and with high quality. It is suggested that the concerned departments revise these standards as quickly as possible.