The 1948 Litang M7. 3 earthquake that occurred in western Sichuan, is the largest strike slip earthquake in the Sichuan- Yunan block in nearly a century. Based on the detailed investigation of the coseismic surface rupture, its precise measurement and statistical analysis were carried out using differential GPS. The results show that the existing length of the surface rupture is 36 km. The northern end of the surface rupture starts from the north of the Wulianghe River and extends southeast along the northeastern margin of Zangba basin and the southeastern margin of Dewu Basin, and extends to the north of Dewu. There is a 3 km long surface rupture gap near Jiaode, and the surface fracture is divided into two sections, north and south. Based on the sectional statistics of the linear density and horizontal dislocation of coseismic surface rupture, it is revealed that the epicenter of this earthquake should be located in the middle of Dewu basin, about 4~5 km southeast of Jiaode. Riedel shear analysis of the surface rupture of the Litang earthquake indicates that the fracture zone is mainly composed of R′shear, characterized by the development of echelon shaped push- up, with a small number of Rshear and T fractures, but lacking any P- type and X- type shear. Among them, the R shear fracture accounts for more than 95%, the dominant direction of which is 318° in the Zangba section (north section), 315° in the Dewu section (south section), and the average R shear direction of the whole surface fracture zone is 316°. At the same time, it is found that the echelon shaped extrusion bulge formed by this earthquake is mainly composed of gentle arc, which is different from the occurrence of a large number of anti- S- shaped extrusion bulges in the surface fracture zone of the 1981 Daofu MS6. 9 earthquake and the 2010 Yushu MS 7. 1 earthquake. It may be closely related to slip rate of strike slip fault. The Riedel shear development along the seismic fracture zone of strike slip fault with strong slip rate should be more perfect, and the extrusion bulge should also be more developed, so it is easy to form anti- S- shape. On the contrary, it is characterized by gentle arc. According to the comprehensive analysis, the distribution of the surface fracture zone of the Litang earthquake in 1948 was mainly controlled by the Zangba basin and the Dewu basin, and the R shear direction of the Zangba section (north section) and the Dewu section (south section) was deviated, which may be related to the development of the two pull- apart basins.