In order to calculate the contact force of the flight lock mechanism, the function and main design basis of flight lock are firstly introduced in this paper. Then the working principle of the flight lock for a specific civil airplane is illustrated, following with the analysis of its force transmission path. Then three calculation methods (engineering method, rigid multi-body model, and flexible multi-body model) are used to compute the contact force between crank and rocker arm. Finally the three calculation methods are compared and analyzed to find out the reasons of the differences between the contact forces for each methods. The results shows that the arm variation caused by mechanism banking leads to the difference between the forces calculated by engineering method and rigid multi-body model. On the other hand, structure deformation is the main factor that causes the difference between the forces calculated by rigid multi-body model and flexible multi-body model. These analysis results can be consulted for the structural design of civil airplane’s flight lock.