Abstract: The mechanical properties and weldabilities of X80 pipeline steel were investigated by testing hardness,tensile strength and impact toughness in this paper.The result showed that the toughness of CGHAZ decreased because of the hardening and embrittling substance appeared in coarse-grained heat affected zone(CGHAZ),and there was a softening zone between the intercritical heat affected zone(ICHAZ) and the subcritical heat affected zone(SCHAZ).The effect of the organization on X80 mechanical properties was discussed also.