The invention discloses a bridge type four-contact point back-to-back gear bending stress testing mechanism and belongs to the field of gear design and manufacturing. The mechanism comprises a support frame and a loading mechanism, wherein the support frame is used for supporting two back-to-back face gears; the loading mechanism comprises four loading rods distributed in a rectangular shape, and a pressure head is mounted at the lower part of each of the loading rods. The two loading rods, corresponding to each other in the length direction, in the loading mechanism, are corresponding to the gear position of the same face gear, and the distance between the inner sides of the two loading rods corresponding to each other in the width direction is slightly larger than the thicknesses of the two back-to-back face gears; the loading mechanism is clamped on the two back-to-back face gears; the contact sides of the pressure heads with the face gears are arranged in a tooth shape; the pressure heads on the loading rods are meshed with gear teeth on the back-to-back face gears. During loading, the back-to-back face gears are mounted back to back to offset the axial forces generated by the face gears; the four pressure heads are in simultaneous contact with the gear teeth of the face gears, so that the stable loading force effect is ensured. The invention further discloses a testing method utilizing the testing mechanism.