Abstract: The present application relates to installation and swap of electric vehicle battery, particularly to a battery pack lock mechanism. The lock mechanism aims at solving the problems that the battery pack is unable to be reliably installed and quickly swapped and to be well protected from loosing during long period of driving. To resolve the above described problems in the prior art, the lock mechanism comprises a housing, a thread bolt, a flange, a spring and a hemp disk assembly which has spike-like protrusions. The flange is unable to rotate around the axis of the bolt, but can slide along its axial direction. The spring can press the flange so that the spike-like protrusions of the flange are engaged with the hemp stopper on the housing, so that the flange and the bolt can't rotate relative to each other, and the bolt can connect the housing to the body of an electric vehicle.