The invention discloses a preparation method of a chelate functional fiber for adsorbing a heavy metal ion. The preparation method comprises the following steps of firstly, adding a matrix fiber intoa reactor, adding a solvent A to swell, and cooling after swelling; next, adding cyanuric chloride and an acid-binding agent, uniformly agitating, carrying out a reaction after uniform agitation, cooling to room temperature after the reaction, filtering, filtering out an obtained product, and washing and vacuum-drying the obtained product in sequence, so as to obtain a cyanuric chloride modified fiber; adding the cyanuric chloride modified fiber into a solvent B to swell, adding a functional reagent after the swelling, uniformly agitating, carrying out a reaction after the uniform agitation, cooling to room temperature after the reaction, filtering, filtering out an obtained product, and treating the obtained product, so as to obtain a product, namely the chelate functional fiber for adsorbing the heavy metal ion. The preparation method provided by the invention is mature and stable, has a simple reaction process, a short time, low energy consumption and a little pollution, is conveniently operated and is easy for treatment.