Abstract: To investigate the effect of aluminum powder particle size on the performance of HMX-based aluminized explosives, the shock overpressure and fireball performance in air blast of HMX-based aluminized explosives with aluminum powder particle sizes of 0.15 μm, 10 μm, and 50 μm were studied. The results indicate that both decreasing and increasing the aluminum powder particle size can enhance the peak value of the near-field shock overpressure. However, neither size change effectively influences the shock overpressure in farther field. The mechanisms by which small and large particle size aluminum powders enhance the shock overpressure differ: smaller particles accelerate the energy release process, while larger particles undergo a process of dispersion followed by energy release, enhancing the energy release at the edge of the explosion fireball. Changing the aluminum powder particle size can extend the positive pressure duration of the shock wave but results in a faster decay rate in the high-pressure segment, leading to a shorter pressure half-life and making it difficult to effectively improve the total impulse of the positive pressure zone or the impulse in the high-pressure segment. Additionally, altering the aluminum powder particle size affects the fireball performance. As the particle size increases, the size of the explosion fireball monotonically increases. However, both overly large or small aluminum powder particle sizes are detrimental to the surface temperature of the explosion fireball.