Regulating rheological properties of water-based drilling fluids has always been a hot topic. This paper proposed a new method for regulating rheological properties of water-based drilling fluids by ultrasonic field. The experimental results showed that the ultrasound increased the viscosity and yield point of bentonite suspension by reducing the particle size of clay, destroying the network structure between clay particles, increasing the mud yield and the cation exchange capacity of bentonite, and promoting the hydration dispersion of bentonite. The change of rheological property showed a memory effect at room temperature and high temperature. Besides, the ultrasonic energy affected the network structure between clays and polymer chains, thus regulating the rheological properties of the bentonite-polymer system. For two types of drilling fluids investigated, the rheology of the poly-sulfonate drilling fluid was regulated by damaging the grid structure between additives and clays by low-power ultrasound and reducing the clay particle size by high-power ultrasound, while the rheology of the deep-water drilling fluid was mainly regulated by disentangling the spatial grid structure between additives. Additionally, ultrasound showed no effect on the lubricity, inhibition and stability of drilling fluids, which proved the feasibility of ultrasound to regulate rheological properties of water-based drilling fluids.