A self-organization method for decision-making service collaboration is proposed based on formal semantic. Firstly, definitions of decision-making service organization are presented, and the theory of Horn clause is introduced as the rule of semantic reasoning. Meanwhile, evaluation algorithms of decision-making service are proposed based on two criterions of decision-making environment and capacity. Finally, the self-organization algorithm is proposed based on the organizing matrix in order to find out the most competent collaboration participants who can satisfy decision-making requirement. Experimental analysis shows the effectiveness and feasibility of the proposed method.