The invention discloses an on-line automobile aluminium alloy hub blank deformation measurement method and a measurement device which relate to the field of automated measurement. The measurement device comprises a test table, a pneumatic clamping mechanism, an air cylinder lifting mechanism, a hub-rotating mechanism, two laser sensors, a motion control module, an industrial personal computer for storing and processing data, and data processing software. By scanning a hub blank in all directions, the measurement device can simultaneously measure the wheel rim deformation and the center axial deformation of the hub blank, thus achieving the effects of high measurement accuracy, more measurement points, high speed and high reliability, automatically measuring the hub blank on line, and increasing the production efficiency of enterprises. The process of measurement is automatic, measurement can be adapted to harsh environments, and cannot be affected by vibration, smoke or humidity, the total measurement time is 30 seconds, the measurement precision is 0.02mm, and the actual demand on measurement can be satisfied.