Abstract: On basis of analying Chengzhaigou ash field,hydraulic construction structure and mining conditions,feasibility study of mining under ash field and dam was done.The ash and its attached hydraulic construction would be influenced grade Ⅱ mining by forecast results of ground movement and deformation.Safety pressure mining under ash field is realized by underground mining technology measures combined with repair and reinforement of surface monitor measures,The economic benefit is significant.Monitoring result shows that coal mining has slightly influence on surface hydraulic construction which maintains normal safety operation.