Open-space emergency evacuation is the movement of people away the threat in the short time. Task allocation is a fundamental research challenge in emergency evacuation domain of multi-agent systems (MAS). This paper proposes the multi-agent task allocation model which is called EV-GAP. Accordingly, the capability of agent was redefined to satisfy the requirement of open-space emergency evacuation. Corresponding the task allocation algorithm based on EV-GAP has is also given. Finally, the experiment of the task allocation of open-space emergency evacuation for a chlorine leakage accident is completed to validate this model.