Traditional space division multiplexing flexible optical network (SDM-EON) only considers the unprotected allocation of fiber core spectrum resources, which lacks of survivability guarantee. This paper proposes an survivable routing core spectrum allocation(RCSA) improved algorithm based on shared risk group. The algorithm allocates the working frequency slots and the protection frequency slots in single multi-core fiber based on the idea of shared risk core group at the same time, and puts forward the priority parameter of service allocation based on the crosstalk mechanism, and the frequency slots allocation scheme which causes the least crosstalk is selected according to the priority. Simulation results show that the proposed algorithm can effectively reduce the bandwidth blocking probability and inter-core crosstalk while ensuring service survivability.