The invention discloses a production method of a low-content-alloy plain carbon type steel plate of 3-8 mm thickness. The production method comprises the procedures of blank production, rolling and separation. According to the blank production procedure, the thickness of the steel plate ranges from 12 mm to 32 mm; the welding speed ranges from 80 mm/s to 120 mm/s; and the welding line energy ranges from 36 KJ/cm<3> to 60 KJ/cm<3>. When the plain carbon type low-content-alloy steel plate is produced through the method, the width can reach 3200 mm to the greatest extent; the yield is high; the cost is low; and rolling mill equipment does not need to be refitted. The process for producing the thin plate through combined means is adopted; dimensions can be adjusted flexibly according to orderrequirements to meet customer requirements; the method can adapt to markets demands for multiple varieties and the ultra-wide specification; the excellent steel plate which is good in surface, plate form and inherent quality can be obtained through rolling; and the production method can be widely applied to bridges, buildings, wind electricity and other manufacturing industries and is good in application prospect.