NASA's Galileo mission to Jupiter has allowed major advances in the understanding of Jupiter's moon Europa. Moreprecise geodetic data make it possible to study the internal structure models of Europa, which may have a complex internal structure. But a subsurface ocean can not be identified just based on the gravity field of Europa. Fortunately, the presence of the subsurface ocean can be supported by the theoretical, geological arguments and magnetic field evidence. Relevant studies on the internal structure models and the subsurface ocean of Europa are briefly described in this article. It is pointed out that the tidal evolution is the most possible explanation of the formation of the subsurface ocean of Europa.