The distribution of P and its effects on the mechanical properties of DD6 alloy were studied in the paper. When P contents were exceed 0.1%, Cr, Nb and Mo were segregated together while Al was rare in the region of P segregation. The region without gamma prime was formed around the region of P segregation. When the content of P was 0.01%, they were segregated in the ruptured interface although O, P and S were the rare elements. The segregatation of P greatlyll degenerated the interfacial strength. The stress-rupture properties and tensile properties were pronounced degenerated with the increments of P.