Abstract: Analyzed here in the essay is the re-crystallization phenomenon of the hi-grade linepipe as being quenched & tempered.The metallographic structure of the hi-grade pipeline-purposed steel is observed via tempering tests as made at different temperatures and with different durations.And the conditions for development of the re-crystallization of the steel are studied,and the effect by the said phenomenon on the mechanical properties of the material is analyzed.Based on the analyses,it is concluded that during a certain time framework,the higher the tempering temperature is,the greater probability for the said re-crystallization will be;at a given temperature,along with the extending of the tempering time,the trend for the re-crystallization will be getting greater and greater;and that moreover the re-crystallization phenomenon shall remarkably reduce both the strength and hardness of the material,however the properties of the material can be improved by means of the re-quenching/tempering treatment.