Abstract:Research purposes: High - speed railway has strict requirements for the smoothness of the rails. Lanzhou - Xinjiang high - speed railway passes across a wide range mudstone region，cut the mudstone will disintegrate when meeting water，and it has large swell - shrink characteristic， so it can cause deformation on the surface of rail. The research on expansive rock ( soil) mainly focuses on ballasted track railway subgrade，lack of research on [allastless track railway subgrade. Therefore，it is necessary to carry out research on expansive mudstone treatment measures in arid area for high - speed railway subgrade，to guarantee the high - speed trains running smoothly. Research conclusions:( 1 ) Tertiary， Cretaceous and Jurassic mudstones have poor diagenesis， soft rock， and developmental joint fissure，it is easily weathered and easily disintegrated when meeting water，with larges well - shrink characteristic，weak and medium expansible. (2) Mudstone foundation treatment should consider the influence of depth of field atmospheric effects. (3) Groundwater is the main factor causing the expansion of mudstone， and foundation treatment needs to take necessary measures such as waterproofing，draining and moisturizing. (4) These research results have been successfully applied to high - speed railway with expansion mudstone subgrade， and accumulated rich experience for similar design，meanwhile can provide the reference for compiling some codes.