Abstract: The underground goaf has brought great harm to the outdoor production, and the roof safety thickness is an important safety guarantee for outdoor production.To study the Luanshya copper strip mining goaf under safe thickness of roof in Luanshya original mining technical conditions and analysis of geological data and in-situ measurement and investigation, and combined with borehole detecting means, such as to determine the distribution of the open-pit mine goaf under.To analyze the underground mined-out area with open state space relations and on the slope of danger division, means of theoretical calculation and numerical simulation of the most dangerous area of goaf roof safety thickness are studied.Results show that within the scope of the most dangerous areas, with different range and different position of mined-out area to analyze the simulation results, the strip mining goaf safety isolation layer thickness is 16 m height(two steps), mined-out area have less effect on the strip mining.