With the application of large diameter steel rod in bridge more and more widely, it is necessary to understand the mechanical properties of 40Cr material used in steel rod, ensure the operation safety of bridge, and provide technical reference for the design of late pull rod. This paper studies the sampling test from the same large-diameter bar, respectively without heat treatment, positive heat treatment, tempering heat treatment and normalizing + tempering heat treatment and other states of sampling test comparison, at the same time, from the different hardness after tempering and whether the forging process is used, respectively, the mechanical properties of 40Cr material have a further understanding, and finally through the metallography group The causes of unqualified impact properties are obtained by weaving comparison, which provides help for in-depth understanding of 40Cr material properties.