Abstract: The model of relationship between screwdown amount of Roll No.2 and residual stress of the pipe is established by taking the actions as below.Based on the stress-strain curve as resulting from the tensile test to the X90M steel plate，and the former parameters of the PWS pre-welding/finish welding operation line，and using the material mechanics theory and MATALAB engineering software， data like the maximum bending torque， and pre-bending radium，etc.for forming process of the said plate is analyzed and deduced.Furthermore，the equation of deflection curve of the plate in the former is found out，and finally the said model is set up.The verification result demonstrates that the relationship model is basically in compliance with the actual production circumstances，being worth using as theoretic guidance to the pipe production.