This paper establishes a new transmission network expansion planning model based on the creditability theory. After solving this model， the optimal planning scheme under fuzzy load can be gotten. The concept of credibility that has physical meaning and strict support in math is induced into the new model to be the evaluation index of different planning schemes under fuzzy uncertain load. Using the“load edges” characteristic in the minimum load cutting problem， the planning model under fuzzy load with a known credibility index can be transformed into the equivalent planning model under interval load. Using the greedy randomized adaptive search procedure combined with the interval most minimum load cutting theory， the transformed model can be solved to get the planning scheme under fuzzy load under a given credibility index. The solution of the new model is independent of the fuzzy load's expression in math， and so it is more adaptive and meaningful. The 46 nodes testing case proves the validity of the model and algorithm proposed.