Abstract: Based on the continuous data of the Abaga Array deployed in the central part of Inner Mongolia in the Xing’an-Mongolia Orogenic Belt, the Rayleigh surface wave dispersion of 5-35 s period was obtained. The high-resolution 3-D S-wave velocity structure of the crust of the study area was further established with the Monte Carlo nonlinear inversion method. The results show the crustal velocity of the Abaga and Dalinor volcanic group is low, and there is an obvious low velocity zone at about 30 km depth in the lower crust, which may be the magma chamber in the lower crust of the volcanic groups. The results also show the low velocity in the crust of Abaga volcanic group, Dalinor volcanic group, Dariganga volcanic group and Ulanhada volcanic group are interconnected. The magma sources of the Abaga volcanic group and the Dalinor volcanic group are in the uppermost layer of the upper mantle. Furtherly it is speculated that the formation of the Abaga and Dalinor volcanic group is due to the upwelling of hot material in the upper mantle, which invaded the crust along the suture zones or faults.