Abstract: On the basis of the appraisal of geological time and the micro-analysis of mineralogical compositions, the analysis of chemical compositions,combining with standard penetration test in situ and soil engineering test in laboratory,the alluvial land of the Quaternary Period is correctly divided into two parts,i,e,two kinds of soil which are belong to the same class with the different geological times and physical mechanical features. The standard values of two kinds of soil for bearing capacity are rationally put forward. These accomulate the experience for the foundational construction at that district,and for fear that the mistaken of stratum division brings about the hidden trouble in economy and safety for engineering construction.