Abstract: In order to study on safety problem of seam mining under river in the hilly area with base rock exposed in Southwest China, based on the geological mini ng conditions, the paper discussed a failure height of the overburden strata and the size of the water prevention safety coal and rock pillars .And in combination with the surface movement and the deformation parameter prediction, the paper analyzed the mining operation affected to the river bed after the mining of the seam and provide d the relevant safety mining technical measures.The results showed that there was a rock pillar with a thickness over 340 m between the max elevation of the water flo W crack zone and the river bed base and the water flow crack zone was far from to the river bed base.After the seam mining, a max horizontal tensile deformation of the river bed was 1.75 mm/m, a max inclined deformation was 5.0 mm/m, a moving deformation value of the river bed was small and would not affect the safety of coal mini ng.