Abstract: The core-mantle boundary (CMB) is one of the most important physical and chemical interfaces in the earth's interior, through which a variety of interactions occur between Earth's core and mantle. These interactions might have great impacts on Earth's gravity field, rotation and magnetic field. The geoid anomalies is an important observation of the earth's gravity field, which reflects significant information of the earth's interior, such as material density anomalies and interfaces, etc. A formula using the geoid anomalies to invert undulations of core-mantle boundary was derived. The large-scale undulations of the core-mantle boundary were calculated by this formula from degree 2 to 4. The result showed that the amplitude of core-mantle boundary undulations reached ±5 km, which corresponded to that obtained by Morelli using seismic tomography, but showed some differences in the worldwild distribution. We also simulated influences of the density anomalies in the core-mantle boundary to the geoid undulation using a prism model with height of 5 km and base length of 1 000 km. The result showed that it was closed to the observed value of geoid undulations.