More and more attention is paid to the uncertainties in the planning and operation of distribution systems. The interval power flow calculation is an important tool to deal with uncertainties. This paper uses complex fans to represent the interval vectors on complex plane, and then proposes a new interval power flow algorithm of distribution networks based on backward/forward sweep method. The proposed algorithm not only is good at dealing with uncertainly but also is suitable to the solution of distribution networks with radial configurations. Computation results of interval power flow with complex-fan representation are analyzed for different load models such as power model, current model and impedance model, and are also compared to those of Monte Carlo simulation method. Test results show that this proposed method has completeness whereas it contains more information about system states under uncertainty than point iteration method, and the results are less conservative. (7 pages)