The mechanical properties, microstructure, grain orientation and precipitates of the pipeline steel X100 with two different chemical compositions were investigated by means of metalloscope, SEM and TEM, etc. Experimental results showed that the X100 pipeline steel made from high niobium+ molybdenum chemical constitution design was prone to obtain balance between strength and ductility. The X100 pipeline steel developed through TMCP had optimal structure consisting of granular bainite, acicular ferrite and less lower bainite, and the ferrite grain size was 3μm approximately. In addition, nanometer precipitates and high-density dislocation in pipeline steel also hardened the parent material actively.