This paper addresses the formation control problem of multiple Euler-Lagrange systems with model uncertainties in the environment containing obstacles. Utilizing the null-space-based(NSB) behavioral control architecture, the proposed problem can be decomposed into elementary missions(behaviors) with different priorities and implemented by each individual system. A class of novel coordination control algorithms is constructed and utilized to achieve accurate formation task while avoiding obstacles and guaranteeing the model uncertainty rejection objective. By using sliding mode control and Lyapunov theory, the formation performance in closed-loop multi-agent systems is proven achievable if the state-dependent gain of the obstacle avoidance mission is appropriately designed. Finally, simulation examples demonstrate the effectiveness of the algorithms. This paper addresses the formation control problem of multiple Euler-Lagrange systems with model uncertainties in the environment containing obstacles. Utilizing the null-space-based (NSB) behavioral control architecture, the proposed problem can be decomposed into an elementary missions (behaviors) with different priorities and implemented by each individual system. A class of novel coordination control algorithms is constructed and utilized to achieve accurate formation task while avoiding obstacles and guaranteeing the model uncertainty resolution objective. By using sliding mode control and Lyapunov theory, the formation performance in closed- loop, multi-agent systems is proven achievable if the state-dependent gain of the obstacle avoidance mission is expected designed. Finally, simulation examples demonstrate the effectiveness of the algorithms.