The invention discloses a stress measurement device based on a deflection method. The stress measurement device based on the deflection method comprises a girder clamping device, a force application loading device, a homogeneous girder and a supporting plate main body, wherein the beam clamping device is fixed on the supporting plate main body; a clamping end of the homogeneous girder is placed on the girder supporting device; a quasi cross laser device is mounted at a force application end of the homogeneous girder; the force application loading device comprises a loading supporting plate, a groups of supports which are fixed on the loading supporting plate, a stress gear, a unidirectional ratchet, a rope and a loading cutting edge; the stress gear and the unidirectional ratchet are fixed on a loading shaft; the loading cutting edge is fixed at the force application end of the homogeneous girder; a pull-pressure sensor is mounted on the loading cutting edge; one end of the rope is fixed on the stress gear; and the other end of the rope is fixed on the pull-pressure sensor. By the stress measurement device based on the deflection method, the homogeneous girder can be in a reliable preset stress state in a large force value range, and the measurement result is accurate.