Abstract: The Xijiawan landslide, a typical loess landslide triggered by HaiYuan Earthquake in 1920 located in XiJi county was investigated in this paper. In order to clarify the formation mechanism of Xijiawan landslide, a series of tests were conducted on the loess soils collected from the main body of slope and surface of rupture in Xijiawan landslide,the possibility of seismic subsidence and liquefaction potential were analyzed, and the works of stability analysis and numerical simulation were done. The results show that the formation mechanism of landslide is the complex of seismic subsidence-liquefaction. When the earthquake happened, the destroy of seismic subsidence occurred on the upper soil of slope. Meanwhile, the saturated loess at the vicinity of lower mudstone built up loess liquefaction instantaneously.