We find that traditional authentication ways donpsilat act well in MANETs for the features of dynamic topology and non-existence of central facilities in mobile ad hoc networks. This paper presents a distributed trust proving language, which is based on role trust. The solution of constructing credential authentication infrastructure and the problem how to perform automated trust negotiation are also discussed. Our design defines roles and policies to make distributed trust negotiation and it can avoid unrelated credential fetching. Simulations show that Our design outperforms traditional trust negotiation ways and is more efficient as a security authentication mechanism in the MANET environments.