The X80 pipeline steel for the west to east gas transmission project was successful produced, based on the hot strip mills equipment advantage. However, the impact toughness was unstable during the production. In this research, optical microscope, scanning electron microscopy (SEM) and energy dispersive analysis (EDS) test were used to study the relationships between different alloy content and microstructure in pipeline steel. What's more, the effect of alloy content on impact toughness in X80 pipeline steel has been explored based on the statistics of alloy composition and the performances in production. The results show that, the alloying elements in X80 pipeline steel can be divided into three categories in this condition. First, Ni, Cu and Mo alloy, it promotes the MA constituents transformation, and leading the impact toughness decreases. Second, Cr and Mn alloy, which have no significant effect on impact toughness. And the third, Nb and Ti micro-alloying, which is particularly improving the impact toughness in pipeline steel.