The invention provides a method for calculating an ultimate safety factor of a lifting lug of a main frame of a fan. The method comprises the following steps: (1) establishing a geometric model of the main frame of the fan and placing the position of a lifting point above the position along the vertical direction of the gravity center of the main frame of the fan; (2) guiding the geometric model into finite element software, defining unit type and material attribute of the main frame of the fan and establishing a finite element model; (3) setting a connecting relationship; (4) applying load and boundary constraint to the finite element model; and (5) calculating the ultimate safety factor of the lifting lug. According to the method for calculating the ultimate safety factor of the lifting lug of the main frame of the fan provided by the invention, the position of the lifting point is placed above the position along the vertical direction of the gravity center of the main frame of the fan when the geometric model is established, and then the finite element model is established for analyzing. In the scheme provided by the invention, when the finite element analysis is performed on the lifting lug of the main frame of the fan, the practical working condition of the lifting lug of the main frame of the fan is fully simulated, so that the problem of inaccurate assessment for the lifting lug stress can be solved.