Abstract: Addressing the challenges of combustion completion in near-stoichiometric hydrogen-oxygen-steam mixtures, micro-mix combustion, with its rapid mixing attributes, emerges as a promising solution. This paper presents a numerical simulation study on the mixing characteristics of a hydrogen-oxygen-steam micro-mix nozzle. Initially, employing a chemical reaction network model, the influence of mixing uniformity on combustion efficiency is analyzed. The results indicate that combustion efficiency increases with enhanced mixing uniformity, thereby establishing the required mixing criteria. Subsequently, computational fluid dynamics (CFD) methods are utilized to investigate the multi-component mixing characteristics within a micro-mix single nozzle and its underlying mechanisms. It is discovered that horseshoe vortices inducing strong turbulence are the primary mechanism controlling the mixing of steam and hydrogen. The uniform mixing of oxygen with the hydrogen-steam mixture is primarily associated with the relative position of counter-rotating swirl vortices and regions of high oxygen concentration.