Wargames are essential simulators for various war scenarios. However, the increasing pace of warfare has rendered traditional wargame decision-making methods inadequate. To address this challenge, wargame-assisted decision-making methods that leverage artificial intelligence techniques, notably reinforcement learning, have emerged as a promising solution. The current wargame environment is beset by a large decision space and sparse rewards, presenting obstacles to optimizing decision-making methods. To overcome these hurdles, a Multi-Agent Deep Deterministic Policy Gradient (MADDPG) based wargame decision-making method is presented. The Partially Observable Markov Decision Process (POMDP), joint action-value function, and the Gumbel-Softmax estimator are applied to optimize MADDPG in order to adapt to the wargame environment. Furthermore, a wargame decision-making method based on the improved MADDPG algorithm is proposed. Using supervised learning in the proposed approach, the training efficiency is improved and the space for manipulation before the reinforcement learning phase is reduced. In addition, a policy gradient estimator is incorporated to reduce the action space and to obtain the global optimal solution. Furthermore, an additional reward function is designed to address the sparse reward problem. The experimental results demonstrate that our proposed wargame decision-making method outperforms the pre-optimization algorithm and other algorithms based on the AC framework in the wargame environment. Our approach offers a promising solution to the challenging problem of decision-making in wargame scenarios, particularly given the increasing speed and complexity of modern warfare.