Human errors are inevitable in steel structure constructing process.They would produce a negative effect on the quality of constructions.There are many factors likely to cause human errors.This paper concludes human-error factors in constructing process of steel structures.Then the importance of these factors can be analyzed by AHP( Analytical Hierarchy Process) method.Afterwards, the importance ranking vector of factors can be acquired.The ranking vector can direct engineers to control human-error factors in constructing process and allocate resource reasonably.Then the safety of steel structures can be ensured.