The invention discloses an automatic measurement device for the thickness of a flexible porous sheet. The device comprises a loading and unloading device, a three-dimensional measuring machine, a measuring platform, a measuring block and a lifting mechanism driving the measuring block to lift; the loading and unloading device automatically grabs a flexible porous sheet workpiece to the measuring platform from a loading work position, then the lifting mechanism places the measuring block on a to-be-measured porous sheet workpiece, the three-dimensional measuring machine is used to measure the thickness of the workpiece, and the loading and unloading device automatically sorts the measured workpieces according to measured results. The automatic measurement device can ensure the high precision of thickness measuring, can not cause any damage on flexible sheet parts during measuring, have functions of automatic measurement and sorting, and have high measurement efficiency.