Abstract: Based on the extensively literature review,this paper summarizes the main issues in the research work of physical sub-ground erosion. The ppaer points out that the engineering geological problems related to the physical sub-ground erosion become more and more serious with the development of various construction projects. However,resulting from the multiplicity,complexity and randomness of the physical sub-ground erosion process,some concepts related to the physical sub-ground erosion are still confusing because of the wrongly or inaccuracy definations,which makes it difficult to academic exchanges.By analyzing of the mechanism,the precise conceptual models ofpiping,seepage compression,contact piping,soil flowing,soil bursting,contact soil flowing,flowing sandandflow solidsare established in this paper,which forms an essential bases of the further research work on the sub-ground erosion.