Abstract: Coal mining under building，railway and water needs to both ensure safety in production，and recover underground resources reasonably.The paper reviewed the research situation of the strength of protective coal pillar in coal mining under building，railway and water.For the shortage in treatment of the protective coal pillar，Advanced methods such as anchor bolt support，grouting，gangue heaping.On the premise of ensuring “three-under” mining safety，more coal resources could be obtained，and then the theories of three methods were studied.Taking coal mining under building，railway and water of Hongliu mine in Yuanyang Lake Mining Area of Shenhua Ningxia Coal Mining Group Co.，Ltd.as a support，the economic feasibility of the protective coal pillars is discussed

Key words: Coal mining under building, Railway and water, Coal pillar strength, Support technology, Anchor bolt, Grouting, Coal gangue heap