This paper presents that the soil cavity is a kind of the environmental-geological problem.The formation and development of the soil cavity arein close relationship with the construction of buildings.Some problemsof the soil cavity still need to be further studied.This paper proposes someviews on its concept,forming conditions,classification,mechanism,infl-uencing formation factors and development of different types.The investiga-tion of their appearance development and distribution is of significance inengineering geology and hydrogeology.