Abstract: The sub-array field patterns of spherical-section phased array were implemented for noninvasive ultrasound liver-tumor surgery. Hereon the sub-array approach includes field calculation, pseudo-inverse method, and genetic algorithm. The sub-arrays uncovered by ribs according to scanned images normally emitted ultrasound. The results from different sub-arrays show quite satisfied acoustic performances, which included qualified focus size and intensity level for ultrasound surgery with single-focus and multi-foci patterns. Moreover they could decrease power accumulation on the ribs, and avoid damaging normal tissues. Thus the sub-array method provides a promising tool for phased array ultrasound propagating through strong obstacles like human rib cage, and that it might broaden the therapeutic area.