In order to reduce spectrum and time fragmentation in elastic optical networks (EON), a fragmentation-aware routing and spectrum allocation (RSA) algorithm is proposed for advance reservation (AR) services. In the stage of route selection, the algorithm uses K-shortest path algorithm to select alternative path set by comprehensively considering the influence factors of path distance, hop count, spectrum resource consumption and adjacency link number. In the stage of resource allocation, local influence factors are used to count the possible spectrum and time fragmentation, so as to reduce the fragmentation of spectrum and time resources around the candidate resource blocks. The overall influence factors are used to concentrate the occupied resources at the boundary of the frequency axis as much as possible, so as to increase the continuity of intermediate idle resources. At the same time, time-domain resource utilization factors are introduced to avoid excessive resource occupation. The simulation results show that the algorithm improves bandwidth blocking probability performance and resource utilization.