<p>The purpose of this paper is to investigate an optimal excess-of-loss reinsurance contract and investment problem involving two mutually cooperative insurers and a reinsurer, within the framework of the Stackelberg game. In the reinsurance contract, the two insurers are permitted to purchase excess-of-loss reinsurance from the reinsurer, who sets the pricing level for the reinsurance. Assume that the two insurers and the reinsurer invest their surpluses in a financial market comprising a risk-free asset and a risky asset, whose price process is described by geometric Brownian motion. Under the criterion of maximizing the expected exponential utility of their terminalwealth, the explicit expressions for the optimal strategies and the corresponding value functions are derived using techniques from optimal control theory and the dynamic programming method. Moreover, to further enhance the research system of reinsurance contract problems within the Stackelberg game framework, we also consider the optimization problem under the proportional reinsurance model. Finally,we present theoretical analyses and numerical examples to illustrate the economic intuition and insights gained from our results. An interesting finding is that the forms of the optimal proportional reinsurance strategy and the optimal excess-of-loss reinsurance strategy are remarkably similar, with differences primarily stemming from the type of reinsurance chosen by the insurers. In addition, we also discover that the two cooperating insurers will develop their own optimal reinsurance strategies based on their respective importance within the cooperative group.</p>