With the rapid growth of wind power penetration, the randomness and volatility of the system are significantly enhanced, which may lead to a great challenge to the optimization of the system’s operation. Power flow calculation is the basis of system operation optimization, but it is difficult to obtain uncertain power flow solutions by deterministic power flow calculation. In this paper, rectangular interval power flow (RIPF) model without Chebyshev approximation is firstly proposed, which narrowes the range of the voltage phase angle of the node and the active power of the branch. Meanwhile, by using the polar interval power flow (PIPF) model based on affine arithmetic, the node voltage amplitude interval can be obtained effectively. Finally, a mixed interval power flow (MIPF) is proposed to obtain bounds of power flow incorporating uncertain wind power generation and loads, and it combines merits of RIPF and PIPF, and greatly improves the accuracy of interval power flow calculation. IEEE 30, IEEE 118 and IEEE 300 are used to verify the effectiveness of the proposed method.