Considering the deficiency of contract net protocol negotiation mechanism convergence and convergent rate research, the Markov chain model of contract net protocol is created under the assumption setting, and it is proven that using previous contract types cannot be guaranteed to get global convergence. Using this as a foundation, the concept of variable neighborhood contract family is proposed. By analyzing the influence of controlling to convergence, the conclusion is obtained that centralized control can guarantee the global convergence and distributed control can guarantee the global convergence with probability, and the calculation method of probability is presented. By taking the advantage of Doebin theory, the convergent rate of variable neighborhood contract family application is analyzed, and the estimates of the convergent rate under centralized control and the upper and lower bounds of convergent rate under distributed control are presented.