Provided is a valve moment quantification determining method. The valve moment quantification determining method comprises the steps that (1) maximum pretightening force Q1 is determined according to allowable axial tensile stress of a bolt, (2) maximum axial pretightening force Q2 is calculated and obtained according to thread bending stress, (3) the Q1 and the Q2 are compared, the maximum moment M1 is obtained according to a moment calculating formula, (4) the maximum moment M2 when the bolt reaches yield stress is calculated by adopting finite elements, (5) the M1 and the M2 are compared, the smaller one is selected as the maximum moment of fastening connection without sealing requests and with sealing requests in valves, (6) the minimum axial sealing force F is obtained according to the minimum sealing specific pressure of fastening connection materials with the sealing requests in the valves, (7) the minimum pretightening force Q4 is obtained according to the work environment of a sealing structure, (8) the minimum moment M3 is obtained according to a moment calculating formula, (9) the minimum moment M4 is calculated by adopting the finite elements, and (10) the M3 and the M4 are compared, and the smaller one is selected as the minimum moment of the fastening connection with the sealing requests in the valves. The valve moment quantification determining method solves the defects that errors are large due to the fact that fastening torque of the valves is applied according to experience.