Controllability of complex networks has important application value in many areas. The minimum driver node set is defined as the minimum nodes required to the control complex network. However, the minimum driver node set of most of network is not unique. Therefore, a random matching method is proposed to obtain different minimum driver node set of a network. Then, the method analyzes the average degree distribution of the collection of minimum driver node sets, and the frequency appears in the collection of the node. It is found that the minimum driver node sets of most networks are distributed tightly. The composition of a driver node set is closely related with the degree distribution of network. The control importance of the node in a network is closely related to the in-degree of node. These conclusions have important research meaning for the controllability of the complex network.