The invention provides a saline and alkaline land improver containing phosphogypsum and trimethylene tetrarea and a using method. The saline and alkaline land improver comprises the following raw materials in parts by weight: 100-400 parts of phosphogypsum, 2-30 parts of humilic acid, 5-40 parts of trimethylene tetrarea, 0.1-1 part of phthalic acid and 0.1-1 part of polyethylene glycol. The using method comprises: firstly, treating the saline and alkaline land by using phosphogypsum and trimethylene tetrarea; and then treating the saline and alkaline land by using trimethylene tetrarea, phthalic acid and polyethylene glycol. The saline and alkaline land improver in the formula matched with the using method can quickly improve the saline and alkaline land which is suitable for crop growth. Moreover, the improver is relatively wide in applying range and suitable for improving salinized soil caused by different reasons in different regions. By applying the improver to the saline and alkaline, the soil structure can be improved, the soil alkalinity can be reduced, the salt elimination rate of soil can be improved, the soil fertility can be improved, the growth of crops can be accelerated, and the agricultural economy can be improved.