In order to compensate the effect of off-axis TMA aerospace mapping camera defocus from engineering practice side, one kind of defocus offsetting compensation mechanism is proposed based on ball screw and rod. The design requirement is analyzed, the adjustment position is determined, and the reliability design and performance indicator detection is carried out. The oscillation angel along the X axis is ±2.7″, the oscillation angel along Y axis is ±3.3″, the residual error is less than 2 μm, the maximum error of sampling is 5 μm, and the mechanism has good self-locking performance, which could be used in off-axis TMA aerospace mapping camera.