Most single-packet IP trace back approaches that have been proposed demand routers to log the packet digests to trace back, which lead to the linear growth of the storage overhead as the forwarded packets are increasing. This paper proposes a novel single-packet IP trace back approach based on the routing path to alleviate the burden of routers. Our approach introduces the relevant theories of label switching path in Multi-Protocol Label Switching (MPLS) and makes use of routing path to set up a Trace back Path (TP). During the trace back process, we can reconstruct the attack path on the basis of label switching mechanism. We use mathematical analysis and simulations to evaluate our approach. Our evaluation results show that compared to HIT and SPIE, two state-of-art single-packet trace back approaches, the storage overhead in our approach is only related to the number of routing paths, no matter how many packets traverse on the paths, and the number of queried routers during the trace back process is only related to the number of hops in an attack path.