Recently, the centralized management in small cell (SC) networks enabled by the existence of a central controller and backhaul links is developed to meet the growing data demand. The effect of load-balancing under the considerations of limited capacity backhaul and co-channel interference is investigated in this paper. Our main goal is to maximize energy efficiency (EE) in SC network through a joint decision strategy consists of user association and radio resource allocation with quality-of-service (QoS) support. To tackle this mixed combinatorial optimization problem, a load-balanced user association and radio resource allocation (LB-UARA) mechanism based on the quantum-behaved particle swarm optimization algorithm is proposed. Simulation results demonstrate that the objectives of QoS satisfaction and energy conservation can be realized via load-balancing procedure in our proposed LB-UARA mechanism.