In recent years, with the evolution of war forms, epistemology under the traditional scientific system has become increasingly difficult to meet the needs of the development of war practice. Complexity science provides new possibilities for understanding war and guiding war practice. In the field of command and control, complexity can serve as a weapon to make opponent decisions more complex, while oneself can easily cope with it. The key to achieving this effect is to break away from traditional decision-making methods and reshape the opponent's decision-making process. To understand the principle of complexity in war and discuss how complexity becomes a weapon, we first need to understand where the complexity of war comes from, as well as the properties and characteristics of complex systems. The traditional thinking method believes that the world is deterministic and humans are rational. Humans can use methods such as "decomposition+understanding+synthesis" to achieve a comprehensive understanding of the world, precise grasp of the nature and operating laws of all things. But there are still many complex systems in the world that have holistic properties, such as the human body, society, economy, war, etc., all of which belong to this category. Complex systems have variable structures, adaptability, uncertainty, emergence, nonlinearity, and other characteristics, and the results are not repetitive and difficult to predict. Social, economic, urban, and intelligent systems all have these characteristics related to humans, but in fact, they are typical complex systems. War is a typical complex system. What people often say about "the contingency in war", "the irreproducibility of war results", "the fog in war", "the unpredictability of troops and water", and so on, are actually describing the characteristics of the complexity of war. The root cause of war or social complexity lies in human cognition. Human beings are not disorganized, thoughtless particles, nor are they lower organisms with simple life logic. Therefore, using simple physical statistical methods can lead to significant deviations. Moreover, human behavior is not only influenced by pure rationality, but also by emotional factors such as personality, emotions, and attitudes that may influence changes in human behavior. Realizing that war is a complex system is a huge progress. Only in this way can we better understand the complexity of war and find ways and means to solve the problem. Instead of simply adopting reductionist methods or simply transplanting physical methods to study war. How to create complexity and turn it into a weapon was originally envisioned by the US military as a "decision center warfare". With the support of advanced technologies such as artificial intelligence, it advocates achieving diversified tactics through the upgrading and transformation of combat platforms and distributed deployment. While ensuring its own tactical selection advantages, it also imposes high complexity on opponents to interfere with their command and decision-making capabilities, occupying an overwhelming advantage in new dimensions. In future warfare, due to the increasing size of the combat system, people and machines are mixed and intertwined in decision-making at all levels, especially with the widespread use of intelligent combat platforms, leading to unprecedented issues in battlefield management. If there are defects in the opponent's information system, they may be constrained by the complexity of their own system. The US military believes that complexity, as a weapon, is meant to make opponents feel complex in one direction, while they can easily cope with it themselves. The key lies in breaking away from the original traditional decision