Abstract: The variance of some physiological indexes of late seedlings of stress-tolerant maize variety "nongda 108" during the half-seawater stress was studied after its germinated seeds and early seedlings were pre-treated for 12 hours by 20% and 70% seawater respectively in order to determine some effectively regulating measures for enhancing salinity-tolerance of seawater-irrigated plant. The result shows: the seawater stresses lead to decline of chlorophyll and carotenoid contents and photosynthetic rate and fresh weight of seedlings, but seed hardening can alleviate above adverse aspects caused by seawater, 70% seawater-treated seeds reduce the damage of chloroplast pigments and photosynthesis and 20% seawater-treated seeds slows down the reduction of fresh weight especially. However, chlorophyll a/ chlorophyll b and root activity and dry weight of seedlings and root/shoot ratio evidently rise in the stress, pre-treatments benefit the ascending root activity and root/shoot ratio, 20% seawater-treated seeds particularly accelerate the increase of dry weight and root/shoot ratio and 70% seawater-treated seeds slightly better promote chlorophyll a/ chlorophyll b and root activity than 20% seawater-treated seeds do. This means that adopting reasonable acclimation in certain developing phases can enhance the adaptability to seawater stress in the growth stages and then improve the using efficiency of seedling to irrigated seawater.