Magnetic Compound Fluid （MCF） polishing is an efficient precision polishing technology. However， the MCF slurry experiences performance degradation during prolonged use. This study investigated the effects of component loss on the polishing performance of MCF slurry and explored the feasibility of restoring its performance through the addition of supplementary solutions to extend its service life. Firstly， polishing experiments were conducted on polymethyl methacrylate （PMMA） using MCF slurry. Changes in the MCF morphologies before and after polishing were observed， and the surface roughness， material removal rate， temperature， and normal force were measured to analyze the performance variations over time. Additionally， supplementary abrasive particle and α-cellulose solutions were added every 10 minutes to evaluate their effectiveness in restoring the performance of MCF and extending its service life. Finally， long-term polishing experiments were conducted to assess the service life of the MCF slurry under the influence of the supplementary solutions. The results indicate that after 60 minutes of continuous polishing， the MCF slurry morphology changed from uniform magnetic clusters to fragmented clusters. The surface roughness reduction rate decreased from 97.06% to 65.97%， showing significant performance degradation. By adding abrasive particle and α-cellulose solutions， the normal force was stabilized at 6.4 N and 7.3 N， respectively， with the surface roughness reduction rate maintained above 85%. Further investigations demonstrated that adding 0.1 mL of supplementary solution every 10 minutes extended the service life of the MCF slurry from 60 minutes to 180 minutes， while maintaining the surface roughness below 0.05 μm and the material removal rate above 1.80 × 10⁸ μm³/min. During the polishing process， the MCF slurry undergoes the loss of water， abrasive particles， and α-cellulose， leading to a decline in polishing performance. By quantitatively replenishing these key components， the polishing performance of the MCF slurry can be effectively restored， ensuring improved polishing stability and significantly extending its service life.