Abstract: Web credibility is an important factor to assess the availability of the portal.In this paper,we propose a usability evaluation model based on the credibility of the theory of web educational portal.Firstly,we give the description of the network of web educational resources.And we define the credibility of the evaluation mechanism from a trusted point of view.And the evaluation algorithm was presented.Finally,the simulation results show that this model can assess the resource of web educational portal effectively and it has a certain significance to improve the site availability.