The invention discloses a pole piece extension consistency control method and a control system, the system comprises a code sprayer, a first camera, a second camera, a third camera and a PLC which are sequentially arranged along a pole piece belt conveying direction, a code spraying port of the code sprayer is vertically downward and is opposite to the upper surface of a pole piece which is ready to enter a front passing roller, lenses of the first camera, the second camera and the third camera are vertically arranged downwards and are sequentially positioned between the front passing roller and the front tension roller, between the front tension roller and the upper and lower rollers and between the rear tension roller and the rear passing roller; the PLC receives the image information collected by the first camera, the second camera and the third camera, identifies the code spraying position on the upper surface of the pole piece, judges the extension state of the pole piece in real time, and sends a control instruction; and the pole piece rolling tension control system adjusts the stretching tension according to the control instruction to keep the extension consistency state of the pole piece. According to the invention, sufficient extension of the tab region can be ensured, and the problem of snake-shaped bending of the pole piece caused by insufficient extension of the tab region or wrinkling of the foil region caused by over-stretching of the tab can be avoided.