The formation control problem for relative translation of the modular spacecraft is studied under a directed graph based on the consensus theory of multi-agent systems. The disturbances on the modules are unknown and associated with the module states. Based on the adaptive gain design, a distributed control algorithm is proposed under the condition that the modules’ masses are unknown. And the closed-loop system is proved to be asymptotically stable via the Lyapunov method. Simulation results of a scenario of six modules are provided to show the effectiveness of the proposed control schemes.