Abstract: Abstract: An intensive study has been conducted of the tectonic characteristics of the middle axial tectonic belt in the Lanping-Simao basin, western Yunnan, through reinterpretation of available DSS (deep seismic sounding) data and petroleum seismic reflection data and an integrated analysis of geophysical, geochemical and mineral resources data. Study indicates that the middle axial tectonic belt in the Lanping-Simao basin is a nearly N-S-trending large-scale tectonic belt integrating the fault zone, extensional structure and deep-seated uplift. The velocity structure of seismic sounding and seismic reflection profile indicate that mantle upwelling occurred at depth in the southern Simao basin of the middle axial tectonic belt. There is difference in dip direction of the fault system in the tectonic belt south and north of the basin. This tectonic belt is closely related to the distributions of mineral deposits, alkaline intrusions and regional geochemical anomalies. On the basis of the above study, combined with the tectonic analysis, the authors think that this tectonic belt is characterized by multi-stage activity and shows the extensional strike-slip characters. During the formation and evolution, the middle axial tectonic belt was dislocated by several nearly E-W-trending linear faults and has the distribution characteristics similar to those of the mid-ocean ridge in terms of the tectono-morphology. The tectonic belt has an important controlling effect on the tectonic evolution of the basin and formation of mineral deposits.