【Objective】There are about 0.66 million hectares of coastal saline-sodic soil in Jiangsu that have not been developed and used as arable land for agriculture. This is because the saline-sodic soil has a higher concentration of salt that requires urgent ameliorating. 【Method】This study used waste phosphogypsum (PG), a kind of by-product from the phosphate industry, to conduct an amelioration experiment of saline-sodic soil in the field. Eight treatments were employed in the field experiment: no fertilizer and PG, fertilizer but no PG, and compound fertilizer + different amounts of PG. 【Result】Results showed that pH was decreased by 0.07～0.40 pH units in the depth of 0～20 cm topsoil treated with PG compared to the control. Soil bicarbonate and sodium ions decreased by 15.81%～43.53% and 17.25%～89.83%, respectively. The concentration of potassium ion, calcium ion, and organic matter in the amended soil treated with PG was increased by 8.17%～384.90%, 59.51%～1977.72%, and 4.51%～19.50%, respectively. Also, the amounts of total N and P in the wheat leaves in the PG treatment were increased by 7.85%～26.21% and 5.02%～35.97%, respectively, and the wheat grain yield increased by 11.41%～45.26%. Overall, PG can be used to ameliorate costal saline-sodic soil with better effectiveness. Mechanistically, the increase in calcium ions occurred as PG exchanged with sodium ions adsorbed in soil, and the sodium ions were leached underground during irrigation and rain to decrease the soil pH. Also, some acid-containing groups in PG were able to neutralize the bicarbonate ions to decrease the soil pH. PG increased the N uptake in wheat leaves and the yield of wheat grain due to the increased P from PG which induced a proportionate uptake of nutrients by the plant. Comprehensively, the best performance was the treatments of 30% compound fertilizer (1050 kg·hm-2) ＋ PG (1125 kg·hm-2) and 30% compound fertilizer (1050 kg·hm-2) ＋ PG (2250 kg·hm-2).【Conclusion】The positive effect of PG should not be considered proportional to the amount applied, because trace hazardous elements in PG could accumulate in the soil which will result in environmental risks and grain safety issues. Thus, proper care should be taken when using high doses of PG for soil amendment.