Efficient energy delivery is increasingly required for clinical HIFU ablation. One typical such approach is volumetric ablation, in which the target volume is divided into different concentric circles (also referred to treatment cells). The focal spots spread uniformly on the circles and each focus is sonicated with the same short time interval. The single-focus and dual-focus patterns were considered to ablate treatment cells with different sizes in simulations. Results show that dual-focus pattern is more suitable for small treatment cells (e.g., 4 mm), while the single-focus pattern is superior for larger cells. Compared with the single-focus pattern, the combination of both patterns can decrease sonication time for volumetric ablation.