The on-orbit servicing task allocation is very important to improve the cooperative work ratio of the on-orbit servicing spacecraft. A discrete particle swarm optimization (DPSO) algorithm is put forward for on-orbit servicing spacecraft cooperative task allocation problems. A new code of particles and new update strategy for the position and speed of particles are applied. By analyzing the critical index factors which contain target spacecraft value, servicing spacecraft attrition and energy-time consumption, on-orbit spacecraft task allocation model is formulated. The simulation results show that the DPSO algorithm has fast convergence, optimization capability, and can solve the on-orbit servicing spacecraft cooperative task allocation effectively.