The relationship between the Tarim platform and the North China plat-form is a very important problem for which geologists show great concern.Based on the aeromagnetic data obtained recently, this paper make a preli-minary discussion and points out that in an area of over 1700km² from LopLake to Alxa there exist four different types of magnetic field, which repre-sent respectively basement lithofacies structures of different natures.The base-ment lithofacies structures shown by magnetic fields suggest that the Tarimplatform might have been linked with the North China platform in Precam-brian or earlier. Nevertheless, as a result of strong tectonic movement in Pale-ozoic, they separated and are hence no longer connected with each other now.