In this paper, an efficient technique with the Bi-CGStab method is proposed for power flow calculation. The proposed method is based on the iterative method for solving a set of linear equations in the Newton-Raphson (N-R) method. The Bi-CGStab method is one of variants of the extended conjugate gradient method that has good convergence characteristics. So far, the direct methods have been used to solve a set of linear equations. However, it is known in numerical analysis that the preconditioned iterative method such as the ILU (Incomplete LU) factorization is useful for solving a set of linear equations. To speed up the power flow calculation, this paper proposes the ILU(p) factorization that is a variant of the ILU factorization. It is created to consider fill-inns of the ILU factorization in a way that some fill-inns are allowed to improve the condition number of the Jacobian matrix of the power flow equation. The condition number affects the convergence characteristics of the iterative method. The effectiveness of the proposed method with the ILU(p)-based Bi-CGStab method is demonstrated in sample systems.