Abstract: Abstract: The Qinghai-Tibet Plateau as an integral unit has continued to be affected by northward subduction of the Indian plate since the assembling of the continent; so certainly the structures of various original terranes have been constantly reworked. As a result, the differences of the plateau as a whole in the E-W direction have been formed. These differences are not in agreement with the constitutions, structures and east-west extensions of the various original terranes. This is not only manifested in the appearance of the N-S-trending fault structure across various individual terranes, but also in the gradual division in the E-W direction. This division is highlighted by the features of the regional gravity and magnetic fields, which is not only the result of the sectional rock magnetism and density variations but also the result of the variations in crustal composition and thickness of various areas and segments in the east and west parts of the plateau caused by different compressions undergone by different parts of the leading edges of the northward subduction of the Indian plate and the differences in block uplift and expansion. Based on the above, the paper analyzes the cause for the E-W division of the Qinghai-Tibet Plateau.The N-S-trending fault structure on the Qinghai-Tibet Plateau is not a local fault in the upper crust but is of deep origin. In the course of northward pushing, the various parts of the Indian plate did not keep abreast of each other. There were differences in pushing speed and subduction depth within the limits of the Qinghai-Tibet Plateau east of the Pamir Plateau. Due to the acceleration of the uplift of the Qinghai-Tibet Plateau, faults appeared on the Qinghai-Tibet Plateau itself. Because the differences have existed since the Miocene, more N-S-trending faults are found at the earth's surface and they extend to greater depths. The Moho depth and crustal thickness are both controlled by these faults, causing the variation in the regional gravity and magnetic fields. At the same time, the E-W extension of the plateau also affects the N-S-trending fault belt.