Geophysical characteristics and basement in the Songpan Garze block and the Western Qinling orogenic belts are studied in this paper. The results show that the basements in the Songpan--Garze and the Western Qinling area belong to Yangtze block. The boundaries are Erdaogou--Yushu--Litang on the southwestern; Qingchuan--Dujiangyan, i.e. the Longmen Mts. fault belt, on the east; and the line of southern Kunlun to Xinghai Xiahe--Xihe on the north. Based on the restrictions of deep seismic sounding and rock physical characteristics under the condition of high temperature and pressure, undulation of the basement in this area is calculated. The depths of the basement are between 1. 3 km to 8. 6 km in the Songpan Garze and the Western Qinling area. The basements are uplift in the areas around Aba Garze--Daofu and Xiahe--Zeku Lanzhou. And the basements are depressed in the areas around Rouergai Tangke--Hongyuan and Huashixia Dari and to the south of Dari. The depth in the Hongyuan area is 8.6 km, which is the deepest place in the Songpan--Garze and the Western Qinling area.