The Xiareer fault, located in the deformation bands of northern and eastern boundary of the Bayan Har block, is situated in the compressive zone between the east Kunlun active fault and Diebu-Bailongjiang fault, also known as the "Maqu seismic gap". Based on the field investigation and remote sensing data validation, it is confirmed that the Xiareer fault is a left- lateral fault with slight dip-slip components trending 310o and extending about 20km. A large amount of horizontal offset landforms distribute along the fault, with a latest left-lateral strike-slip of 3.5 ~ 5m, free of vertical offsets. Two trenches excavated along the direction perpendicular to the fault reveal that the fault cuts through the Late Quaternary stratum, covered with palustrine peat-layer on the surface. The relevant data ageing study reveals that the horizontal left-lateral slip-rate is approximately to 7. Imm/a. The fault has a good coherence in the kinematics characteristics with the Maqu fault of East Kunlun Active Fault, and it is possible that the Xiareer fault is closely interrelated with the East Kunlun Active Fault, as a subsidiary fracture belonging to the east Kunlun active fault.