By optimizing the setting of the relay protection, it is possible to improve the coordination of the relay protection in the power system and reduce the relay operation time, so that the reliability of the power system is improved. In this paper, the calculation of inverse time overcurrent protection is transformed into nonlinear programming problem with multiple constraints for the coordination of the relay protection in distribution network. In order to solve this problem, an inverse-time overcurrent protection coordination scheme based on improved symbiotic search algorithm was proposed. The simulation results of SOS-AA algorithm was analyzed in two different cases. The results proved that the proposed scheme is better in terms of the optimization quality, convergence and efficiency. The coordination scheme based on SOS-AA algorithm can improve quick action performance.