In the paper,the method of sectionnode control is first proposed to solve the problem of 3D mesh autogeneration in FEM analysi s when geological strata are complicate and largescale underground grottos are excavated.The geological exploratory sections are used as chief control section s,in which a small amount of data preparation is needed.The 3D mesh is generat ed in the whole calculating region by means of different mergences,linkages and interpolations.Several engineering calculation illustrations show that this meth od is simple,more applicable and efficient. 