The width of the steel plates to be pretreated in this line is no more than 4,000 mm, the length is no more than 18,000 mm, and the thickness is 6 to 50 mm. The rust removal level of this line complies with GB8923-88 Sa2.5; the paint film thickness is 15 to 25; the surface roughness is 40 to 70; the pretreatment speed is about 4m/min.