Abstract: Described in the article are the changes of yield strength，tensile strength，yield ratio and impact toughness of the X90 linepipe-purposed steel before and after being turned into the pipe. Analyzed are the reasons for these changes. Accordingly，control values of the above mentioned properties of the X90 steel plate are determined.Related test results show that after the said steel plate being processed into the pipe，both the yield strength and the tensile strength go up，and the average gain of the tensile strength is greater than that of the yield strength，whereas the impact toughness goes down. The reason for such property changes is the influence on the steel plate by the working hardening，and the influence itself depends on the chemical composition and the rolling process as used for the steel plate.