Abstract: Land-conserving plays an important role in the building of resource-conserving society. The relationship among dump formation and rock-earth volume in opencast mine were discussed by geometry analysis. Then the correlation model was constructed and proved by the example of Shangyao Dump of Anjialing opencast mining in Pingshuo. As a result, it will get the aim of land-conserving and insure the stabilization of dump if the relationship between the length of slope and the width of step is taken into account logically when the Dump is designed.