We develop and analyze a time-domain bi-level power control scheme using Almost Blank Subframe (ABS) for downlink cross-tier interference mitigation. Even for only one femto cell and macro cell, the optimization problem given rate constraint is nonconvex. We prove that by relaxing the integer requirement for subframe division, the optimal strategy is using either power control or ABS individually, and a joint scheme is not needed in the optimal solution. Imposing the integer subframe number requirement, this conclusion is no longer true. However, we show that the optimal solution also assumes simple structure by choosing from one of three feasible solutions. Simulation results show that the joint power control and ABS scheme outperforms traditional single-level power control scheme for downlink cross-tier interference mitigation with low computational complexity.