Since the asphalt overlay of freeway in Hubei Province was opened, it appeared undue early diseases. The diseases mainly appeared in the surface layer. Through the disease investigation, construction data lookups and on-site samplings of SMA-13 surface layer, the three main reasons of early diseases are indicated. They are unclean raw materials, loose control of mixture proportion and unreasonable construction site management. This paper analyzed the generation mechanism of diseases in SMA pavement from every involved respect. At last, the suggestions about const...