Abstract: The study on trust relationship among grid entities is the hot point of grid security because of the security problem resulting from the dynamics and the uncertainty of grid technology. According to the characteristic of grid technology, an improved layered trust model that is based on domain is presented under the study of the available trust relationship. This model is used to deal with trust relations among entities in the grid environment. The model takes different ways to deal with trust relation in and between domains, the update mechanism of the trust value and the attenuation factor of time. A preferable performance in availability of the model is indicated through analysis and experiment simulation, and it is the efficient supplement to trust models in grid.