A cooperative apparatus and a resource block allocation method thereof for use in a wireless network are provided. The wireless network comprises a plurality of femtocells. The cooperative apparatus groups the femtocells based on signal interferences between the femtocells. The femtocells with higher signal interferences are joined to the same femtocell group. The cooperative apparatus averagely allocates resource blocks to the femtocells in the same femtocell group, and randomly allocates resource blocks to different femtocell groups.