On the basis of geological investigating work and experimental studies on slide zone soil of one landslide in Tibet，the authors analyzed granulometric composition，clay mineral composition and physical and mechanical properties for the soil in the slide zone． The soil samples are gravel containing fine particle． Particles larger than 2 mm occupy the main proportion with the content 51. 5%--68. 5%． The relative content of clay minerals is low． The clay minerals are illite smectite mixed layer and kaolinite，and their relative contents are 6% --13% and 4%-11%，respectively． The main mineral ingredient is quartz and the relative content is over 30%． Therefore，the soil’s hydrophily is poor． The cohesion and internal friction angle are high，causing preferable physical-mechanical features of slide zone soil． On the basis of the obtained data，the landslide stability is evaluated by means of limit equilibrium method． The safety factors are 3. 191 and 1. 92 respectively under both natural and normal water level conditions． The study results show that the landslide is stable． It can provide the appropriate basis and reference for landslide stability evaluation and landslide control in Tibet．