In order to achieve fast assignment of gravity anomaly for skip-gliding trajectory in hypersonic speed, an adaptive grid assignment model was proposed, and the generalized extension approximation algorithm was optimized based on the inverse distance weighting theory, the approximation error of the model was analyzed as well. The space of the assignment model was divided at two levels. The first level grid was divided according to the standard ballistic airspace, and the second level adaptive grid was built online according to the actual trajectory of the missile. According to the data of the first level grid nodes, the data of the second level grid nodes were calculated by optimized generalized extension approximation algorithm. Finally, the gravity anomaly value of the actual ballistic points was calculated by interpolation algorithm within the second level grid. The simulation results show that the approximation accuracy of the optimized generalized extension adaptive grid model is higher than that of the general assignment method under the grid with same size. Under the same precision, the maximum grid length of the assignment model is larger than the general assignment method, which can the number of grid division and the amount of data stored on the missile.For the different gliding direction and gliding distance of the jump gliding trajectory, the drop point deviation corresponding to the gravity anomaly approximation error less than 5 m. On the premise of satisfying the calculation speed, this assignment model improves the accuracy of the traditional assignment method and reduces the amount of storage on the missile, and has a certain value of engineering application.