Line loss rate is a key indicator to reflect the management level of grid enterprise in the process of power transmission.Because of a variety of reasons, it is difficult to compute the exact value according to the formula of line losses in 380V Distribution Power Grid.However,we can obtain the respective parameter's range by using the correct investigation methods and compute the interval of line losses under the uncertain situation.In this paper, we fined the grey model of line losses and proposed the formula of covered operation, and a modified case was to be verified the feasibility of grey model in real applications.