In view of the uncertainty factors in high voltage transmission network， an interval DC power flow algorithm is proposed in this paper which using interval algorithm to analyze the uncertainty problems. Taking the uncertainty of injected node active power into account， interval linear equations are solved with interval Gauss elimination method in the proposed algorithm. The bounds of voltage phase angles and branch active powers， as interval solutions of interval DC power flow equations are obtained. Taking IEEE 30-bus system as test systems， the results of the proposed algorithm are compared with the results of Monte Carlo simulation method and it shows the validity and practicability of the proposed algorithm.