This paper proposes a physical-security-based routing algorithm for a wireless multi-hop network in the presence of multiple colluding eavesdroppers. The algorithm firstly obtains end-to-end secure connection probability (EESCP) without the knowledge of the locations of the eavesdroppers as well as the channel state information(CSI). Then, a shortest-path routing algorithm, which can be simply realized using traditional Bellman-Ford method, is introduced by solving the EESCP maximization problem. Furthermore, an improved Bellman-Ford algorithm is designed to get higher security level. The simulation results demonstrate that the proposed algorithm can be applied to a network of arbitrary size, and has significantly higher security performance compared with the traditional ones.