In order to handle the uncertainty problem in high voltage transmission system DC power flow calculations， an interval algorithm of DC power flow calculation using Krawczyk algorithm is proposed. An interval vector containing the hull of the solution set is obtained by interval Gaussian elimination method， and is used as the initial value of Krawczyk iteration. The inverse of center of interval coefficient matrix is used in the iterative calculation to reduce the effect of dependence. The reduction range of the infinite norm of interval solution vector is served as termination criterion. The proposed algorithm can obtain sharper bounds of the hull of the solution set of interval linear equations than interval Gaussian elimination method. The proposed method has been tested on Garver-6 system. The results demonstrate the effectiveness and practical value of the approach by comparing with the results of Monte Carlo simulation and Gaussian elimination method.