A pull-up fitness exercise machine includes a base, a cantilever, a cantilever aligning unit, a pulling and latching unit, an assisted pushing unit, a limit assembly and a support plate. At a low static position, the support plate is acted by the limit assembly and fixed to a bottom position of the base, such that only after a specific gravitational force is exerted onto the support plate, and the cantilever is pulled downward, the support plate is released from a locked status. In addition, a central column at the bottom of the base has an inverted hook member operating together with a circular ring installed at a corresponding position of the support plate to form a secondary safety device to prevent the support plate to have any unexpected lifting movement and ensure the safety of use.