Regulation of the optical path difference (OPD) is a significant part of space distributed optical interferometers. The OPD is required to regulate within 0 ± 20 nm in this paper, which can hardly be satisfied by the control capability on spacecraft bus level in a real world mission. A dual-stage regulate method based on the robust integral control is proposed to regulate the OPD arising from relative motion, especially relative velocity residual between two formation-flying satellites. A classic PID control law is designed for the coarse-level motion platform, which is employed to regulate the OPD within micrometer order. And a robust integral control law is designed for the fine-level motion platform, which is used to regulate the residual OPD within nanometer order. The effectiveness of the proposed dual-stage control scheme is verified by numerical simulations, and the OPD can thus be regulated within 0 ± 10 nm in one side after about 4.6 s, so that 0 ± 20 nm OPD can be guaranteed. Regulation results for the non-robust integral control are also given as comparison.