The invention provides a method for improving a saline and alkaline land by using ardealite, tetrametilenpentaurea and biological bacteria. The method comprises the following steps: firstly, treating the saline and alkaline land by using ardealite; then treating the saline and alkaline land by using tetrametilenpentaurea and a curing agent; and finally, treating the saline and alkaline land by using materials which are treated by a mixture of straws and microorganisms. With the adoption of the method for improving the saline and alkaline land, provided by the invention, the saline and alkaline land can be rapidly improved and is suitable for the growth of crops; an application range of a modifying agent is relatively wide and is applicable to soil improvement of soil alkalization caused by different reasons in different regions; and the modifying agent is reasonably applied to the soil so that the soil structure can be improved, the soil alkalinity is reduced, the salt rejection ratio of the soil is improved, the soil fertility is improved, the growth of the crops is accelerated and the agricultural economy is improved.