A vehicle frame assembly includes a forked first frame member coupled to a second frame member via a coupling device. The coupling device includes first and second tab units, and a fastening unit. The first tab unit is mounted on the first frame member, and includes a pair of first tabs, each formed with a first coupling hole and an angle-adjusting hole unit. The second tab unit is mounted on the second frame member, and includes a pair of second tabs, each formed with a second coupling hole and an engaging hole unit to be registered with the first coupling holes and the angle-adjusting hole units, respectively. The fastening unit includes a first fastener extended removably through the first and second coupling holes, and a second fastener extended removably through the angle-adjusting hole units and the engaging hole units.