During the water level design process of lock with water saving basins (WSBs), it's an important part that to determine the water level and head of the WSB, and there are many influencing factors in the process. This paper derives and establishes calculation formulas for evaluating the water level and the water head of the single-step lock with WSBs, which integrates the total head of ship lock, the upper and lower stream water level variation, the number of the WSB levels and area of the WSB, and the remaining head. On the basis of formulas, the influence of factors such as the upper and lower stream water level variation, the number of the WSB levels and the area of the WSB on the water level and the water head of the WSB are analyzed, and the control conditions of the integrated and decentralized arrangement of WSBs and water-saving rates of replenishment and overflow operations are calculated. The results show that when total head of the lock is constant, head of the WSB decreases with the increase of the area of the WSB and the number of the WSB levels, and the increase of the number of the WSB levels is greater than the increase of the area of the WSB; when the number of levels and area of the WSB increase to a certain level, the reduction of the water head of the WSB becomes slow; the highest and lowest water levels of the WSB are controlled by the maximum variation of the downstream and upstream water levels respectively. Finally, the water levels and the water head of difference WSB schemes are calculated and compared in a 60m single-level ship lock, and a reasonable water level scheme of WSB is proposed.