Abstract: A vehicle roof rack structure includes a first clamp assembly, a second clamp assembly and a driving member. The first clamp assembly has a first positioning member. The second clamp assembly, aside to the first clamp assembly, has a second positioning member with a second-clamp-assembly bevel surface. The driving member for driving the second clamp assembly includes a screw bar, a driving block and a vehicle-roof bar. The screw bar engages the first and the second positioning members. The driving block, engaging the screw bar, has a driving-block bevel surface to contact the second-clamp-assembly bevel surface. The vehicle-roof bar has an end to mount the first and the second clamp assemblies. When the screw bar rotates, the screw bar drives the driving block to drive the first and the second clamp assemblies to clamp or release the vehicle-roof mounting rack in between.