The structure and mechanical properties of pipeline steel X80 through HTP rolled into 16mm thick slab were tested. The results show that the yield strength of tested has reached above 600Mpa, and the ratio of tensile strength to yield strength is 0.86, and duetile brittle transition temperature is lower than -60°C , and good strength and toughness are obtained. Low content of P, S, high content of Mn and fine microstructure have good effect on reducing the ductile-brittle transitiop temperature. Two different precipitations are observed in pipeline steel X80, a class of TiN precipitations is mainly and a small number of (Nb, V)(C, N) complex precipitations in the TiN around, and the other for large number of NbC precipitations and a small amount of TiC、VC and simultaneous deposition of the complex formed precipitations. Remarkable strengthening and grain refinement can ne caused by these precipitations.