Magnetic compound fluids （MCFs） have been shown to exhibit excellent polishing performance. However， problems with water wastage in MCF slurries during the polishing process can deteriorate their performance. This increases the costs of polishing using MCF slurries significantly， which substantially limits the application of MCF polishing technology. To address the issue of water loss in an MCF slurry， the relationships between the MCF's water content and the morphology， polishing temperature， normal pressure， and polishing quality of the MCF were investigated. The mechanism of the influence of moisture on polishing quality was also evaluated. First， the influences of different water content levels on the polishing properties of the fluid were analyzed. Additionally， the morphological characteristics of the MCF slurry before and after polishing were observed using industrial cameras. Then， the polishing mechanism of the MCF with varying water contents was examined by summarizing the internal relationship between temperature increases， the state of the MCF， and the force exerted in the polishing process as well as the quality of the resulting surface. Finally， the shortened lifespan of the MCF slurry was effectively alleviated by adding water. The following key results were obtained. （1） The initial polishing was better when the water content of the MCF polishing liquid was maintained at 45%. After 10 min of polishing， the surface roughness of the workpiece decreased from 0.410 μm to 0.007 μm using the initial MCF slurry. In contrast， it decreased from 0.576 μm to 0.173 μm using the MCF slurry that had been used for 50 min. The polishing performance of the MCF significantly decreased with increasing polishing time. （2） The ability of the MCF to recover worsened with decreasing water content in the slurry， which in turn affected its polishing performance. （3） The rate of decrease of the roughness of the polished surface after 60 min of polishing increased from 69.97% initially to 86.69% after adding water to the MCF slurry. The rate at which material was removed increased from 0.95×10⁸ μm³/min to 1.45×10⁸ μm³/min， and the normal force of the polishing increased from 3.7 N to 4.2 N. When water is added to an MCF slurry during the polishing process， maintaining a water content of approximately 45% can improve the long-term stable polishing ability of the slurry and extend the service life of the MCF effectively.