The invention discloses a machining device for back plates of liquid crystal displays of ultra-thin smartphones. The machining device comprises a bottom plate, a fixed seat, a horizontal cylinder, a vertical cylinder, a support plate as well as a left guide rail seat and a right guide rail seat which are fixed on the bottom plate, wherein the support plate is located between the left guide rail seat and the right guide rail seat; the vertical cylinder located below the support plate is mounted on the bottom plate, an ejection rod of the vertical cylinder is connected with the support plate, and an elastomeric pad covers the upper surface of the support plate; a left through hole strip and a right through hole strip are formed in the left guide rail seat and the right guide rail seat respectively, a rolling shaping bar is located above the support plate, two ends of the rolling shaping bar are embedded in the left through hole strip and the right through hole strip, a connecting shaft is located on the left guide rail seat and the right guide rail seat, and two ends of the connecting shaft and the two ends of the rolling shaping bar are connected through a left connecting block and a right connecting block. With the adoption of the machining device, efficient and high-quality leveling operation can be realized for the back plates with large-range warpage, the leveling effect is good, the efficiency is high, and products have stable quality and cannot be broken easily.