Abstract: Analyzed are the fracture morphology and rupturing g enerating process of the 27SiMn material asresulting from blow-out of the hydraulic cylinder. Based on the analysis result，the hi-strength/toughness，low carbonequivalent XG720 steel is proposed. Also analyzed are the chemical composition， mechanical properties，machinability and weldability of the XG720 steel. As a result，it is identified that the XG720 steel mostly featuresrather high strength and good toughness after being hot-rolled and normalized， while after being cold-drawn， itsproperties are quite better than the as-cold-drawn 27SiMn steel，having met the special requirement for the precisionsteel pipe.