The present invention discloses a method and system for controlling axial length of an ellipsoidal shell based on liquid volume loading. The method includes: determining the volume calculation models of an unformed prefabricated shell and a formed ellipsoidal shell; determining a calculation model of a volume difference between the unformed prefabricated shell and the formed ellipsoidal shell; determining a structure size of the unformed prefabricated shell according to a target axial length of the formed ellipsoidal shell; obtaining the volume difference between the formed ellipsoidal shell and the unformed prefabricated shell, and recording the volume difference as a target volume; injecting liquid into the unformed prefabricated shell with target volume to obtain the formed ellipsoidal shell. The forming process in the present invention is simple and easy to implement without considering differences in materials and wall thicknesses and can control and adjust the axial length dimension accuracy of a shell.