Routing, modulation and spectrum allocation(RMSA) has become one of the main methods to improve the utilization of spectrum in elastic optical networks(EONs). Aiming at the routing of RMSA, a multi-hop routing, modulation and spectrum allocation(SDLN-MHRMSA) algorithm based on the shortest distance and the least nodes is proposed. The algorithm divides the path of the shortest distance and the least nodes into a certain number of sub optical paths through the optical electric optical converter with multi-hop routing, and then allocates the spectrum for the traffic request according to the distance adaptive modulation technology on each sub optical path. Theoretical analysis and simulation results show that the proposed algorithm has better performance in blocking rate and spectrum resource utilization than the traditional RMSA algorithm based on the shortest path.