Mesozoic granite is widely distributed in southeast China, which can be divided into Nanling and southeast coastal granitic belts. Due to the effect of tectonism, the depth of Moho and the thickness of lithosphere together with the emplacement age of granite bodies decrease eastward, but the temperature at the depth increases eastward. Radioactive heat-producing element content determinations of granites from surface and drill holes within Nanling region and Southeast coastal region show that the average radioactive heat generation ratios are 5.18 and 3.01 μW/m³, respectively, and that the Fogang granitic body exhibits the highest value of 7.56 μW/m³. In addition, the thermal contribution rate mainly comes from the radioactive decay heat of Th and U with ⁴⁰K thermal contribution being less than 10%. The new data obtained by the authors, in combination with previous geological, geophysical and geothermal data, indicate that the contribution rate from the crust to the surface heat flow in Nanling region and Southeast coastal region is about 60%~65% and 40%~45%, respectively. The result suggests that Nanling region is of “hot crust-cold mantle” type and the Southeast coastal region is of “cold crust-hot mantle” type lithospheric thermal structure.