For the connecting rod bushing forged by tin bronze CuSn8P, the offset backward spinning process was simulated under different thinning rates, spindle speeds and axial offsets, and the influences of thinning rate, spindle speed, axial offset and their interaction effects on inner diameter tolerance and straightness error were obtained by combining with complete factorial test to deal with the data of simulation results. The results show that there are interaction effects in factors of offset backward spinning for the connecting rod bushing forged by tin bronze CuSn8P. In the influence of straightness error, the third-order interaction effect even exceeds the second-order interaction effect. The order of significant influence on inner diameter tolerance is axial offset>spindle speed> thinning rate, and the order of significant influence on straightness error is thinning rate>axial offset>spindle speed. Thus, increasing the thinning rate reduces the inner diameter tolerance and straightness error, and increasing the spindle speed and the axial offset reduce the inner diameter tolerance to a certain extent, but they also increase the straightness error.