The invention belongs to the technical field of precision machining and provides an opposite grinding device and an opposite grinding method for improving gear machining precision based on the meshinggear tooth face deviation error homogenization effect to further improve the ultra-precision gear machining precision. The device comprises a driving friction wheel, a driving belt wheel, a transmission belt A, a connecting rod A, a rotation shaft section A, dense ball shaft sleeves, an opposite grinding gear A, an oscillating bar tension spring, a driven friction wheel, a driven friction wheel oscillating bar, a driven belt wheel, a transmission belt B, a connecting rod B, a tensioning wheel compression spring, a tensioning mechanism, a rotation shaft section B and an opposite grinding gearB. According to the device, the gear tooth pitch, the tooth profile, the spiral line and the radial jump deviation can be synchronously reduced through opposite grinding, the machining cost is low, the effects of improving the gear tooth pitch, the tooth profile, the spiral line and the radial jump precision are obvious, and the roughness error of the tooth face can be reduced. The provided gear opposite grinding method can be popularized to opposite grinding of high-end transmission device gear pairs, and good market application prospects and popularization value are achieved.