Abstract: The early Cretaceous mafic-acidic igneous rocks from the coastal area of Zhejiang Province constitute the typical composite lavas flow and dikes. The basalts and diabases in the early Cretaceous composite lavas flow and dikes are highly enriched in large-ion lithophile elements (LILE). The working of source enrichment alone could not result in such high abundance of LILE and related variation, and the contribution of crustal contamination should be considered. Relationship between ratios of Rb/Y and Nb/Y (with Rb/Nb ratios varying from 0.4 to 9.1) indicates that the tholeiitic magma might interact with the rocks of mid-upper crust. Calculated average melt density of the tholeiitic magma by its chemical composition is 2.678g/cm3 . This is approximately corresponding with density of the mid-upper crust of the coastal area of Zhejiang Province. Assuming that the rising of magma was driven mainly by float force resulted from density difference between magma and surrounding rocks of crust; it would stagnate at the level of neutral float. According to the hydrostatic pressure equilibrium between magma and surrounding crystal rocks, it is estimated that the tholeiitic magma from the mantle source would continue to rise till it was trapped by mid-crust at the depth about 16.3 km below the surface. Meanwhile the magma was contaminated by the crustal materials.