A gravity modelling of the Spanish Central System Crust has been carried out along two profiles. In order to constrain gravity modelling results Profile I runs along the Toledo-Salamanca seismic profile. Profile II trends perpendicular to the range trend. The seismic crustal model reproduced the Bouguer anomaly in a suitable way. The crust is thickening and the crust-mantle boundary descends between the Duero Basin southern zone and the central part of the Madrid Basin, from 32 to 35 km. Thickening occurs mainly in the middle crust, whose upper and lower boundaries exhibit a different geometry. The upper boundary appears upheaved, as well as the upper crust beneath the Spanish Central System. Two reverse faults limit this uplifted block. The lower boundary Is deflected 3 km, like Moho surface. This crustal structure suggests that the Spanish Central System represents a crustal pop-up, related to a deep detachment, south-dipping, located between a depth of 12 to 20 km. Terctiary compression results of crustal shortening in the Iberian Plate interior.