The invention relates to a coastal saline-alkali soil improving method and belongs to the technical field of saline-alkali soil improvement. The method comprises the following steps that 1, a drainage ditch is built; 2, soil tillage is conducted; 3, drip washing and salt elimination are conducted; 4, the third step is repeated until the salinity and alkalinity are lowered to the specialized range; 5, resin is poured into saline-alkali soil to form a salt prevention layer; 6, the bottom of the drainage ditch is filled with filling materials; 7, soil conditioner and organic fertilizer are applied to the soil. According to the coastal saline-alkali soil improving method, firstly a drainage system is built, soil tillage is conducted, then the tilled soil is subjected to drip washing, after drip washing is conducted repeatedly, the salinity and alkalinity of the soil are lowered quickly, and the method accords with the growth of general plants; due to the fact that fertilizer in the soil is also taken away at the same time of drip washing, the soil is poorer and easier to harden, and therefore, complex fertilizer operation such as application of biological fertilizer is also conducted after drip washing on the soil, so that the fertility of the soil is improved quickly, and the method is suitable for the growth of plants.