Mobile ad hoc networks (MANET) is a new networking paradigm for wireless hosts. Because of infrastructureless, self-organization, dynamic topology and openness of wireless links, the routing security problem in MANET is more seriously than in wired networks. Optimized link state routing (OLSR) (T. Clausen et al., 2003) is proposed by IETF's MANET Group at 2003. In OLSR, neighbor detection is not invulnerable when two bad nodes perform wormhole attack. Furthermore, OLSR's security cannot simply rely on IPSec, because OLSR's packets are often broadcasted and IPsec provides end-to-end security. In this paper, we propose a solution to secure OLSR, which apply the wormhole detective mechanism and authentication to strengthen the neighbor relationship establishment, and use hash-chain and digital signature to protect the routing packets.