The invention discloses a modification method for heavy metal ion adsorbent illite. The modification method comprises the following steps: (1) firstly, pulverizing illite raw ore by a pulverizer to enable the granularity of the illite raw ore to be not less than 120 meshes; (2) measuring 50mL of ethyl alcohol and adding 5mL of silane coupling agent to the ethyl alcohol, and then, performing ultrasonic treatment for 20min; (3) adding 40g of pulverized illite raw ore to ultrasonically treated solution, and stirring a mixture in a thermostatic water bath of 55 DEG C for 3h; (4) washing deposits in the mixture after water bath with the ethyl alcohol, and then, performing suction filtration, drying and milling to obtain a powdery finished product. The invention provides the modification method for heavy metal ion adsorbent illite with the advantages that the investment is low, the energy consumption is low, the preparation method is simple, the treatment effect is good and the operation is convenient, and by applying the produced modified illite to remove heavy metal ions in waste water, the removal effect is good, and the operation is convenient.