Objective: The rheological control of drilling fluids under high-temperature conditions at the bottom of deep wells remains a challenging issue. Viscosity reducers are considered effective agents for adjusting the rheological properties of drilling fluids. However, research on anti-high-temperature viscosity reducers is relatively limited in China. In this study, an anti-high-temperature viscosity reducer named GMZ was synthesized, characterized, and its performance evaluated to elucidate its working mechanism. The objective was to develop a more reliable, efficient, and environmentally friendly viscosity reducer suitable for domestic drilling operations. Methods and Results: Infrared spectroscopy confirmed that glycerol, zirconium sulfate, and polymaleic acid had successfully reacted to form the target compound GMZ. Thermogravimetric analysis demonstrated that GMZ exhibited excellent thermal stability, with a mass retention rate of up to 55% even after calcination at 800?°C. Performance evaluation tests revealed that GMZ could withstand temperatures as high as 210?°C, achieving a viscosity reduction rate of 82.61% in the base slurry. Furthermore, GMZ showed good compatibility and maintained effective viscosity and shear-thinning properties in both sulfonated and desulfonated systems. Biological toxicity testing indicated that the LC50 value of GMZ exceeded 40,000 mg/L, which satisfies the national regulatory requirements for biological toxicity in water-based drilling fluids used in first-class marine areas. Particle size and zeta potential analyses showed that the addition of 2% GMZ significantly reduced both the particle size and zeta potential of bentonite slurries after high-temperature aging at 210?°C, indicating enhanced dispersion and mitigation of high-temperature-induced particle aggregation. Optical microscopy and SEM observations further confirmed that GMZ improved the dispersion of bentonite particles. XRD and TEM analyses revealed that GMZ"s cations replaced aluminum ions at the edges of clay layers, increasing intermolecular repulsion and contributing to its high-temperature resistance and viscosity-reducing effects. Conclusion: GMZ has already achieved industrial-scale production and shows promising application potential. However, its performance under high-temperature and high-density field conditions requires further validation through actual field operations.