The invention provides a nylon-copper composite capable of preventing marine biofouling for a long time. The nylon-copper composite is prepared from raw materials in percentage by mass as follows: 5%-10% of metal copper powder, 0.1%-1% of a coupling agent, 1%-20% of sodium carboxymethylcellulose powder and the balance of nylon powder. The invention also provides a preparation method of the nylon-copper composite. Nylon powder, metal copper powder and sodium carboxymethylcellulose powder are put in a drying oven respectively to be dried, the dried nylon powder, metal copper powder, sodium carboxymethylcellulose powder and the coupling agent are put in a high-speed mixer in a preset proportion to be mixed uniformly and then taken out, and nylon-copper composite powder is obtained; the nylon-copper composite powder is added to an extruder and extruded after being subjected to melt blending, the extruded product is subjected to water cooling and granulation by a granulator, the prepared granules are dried and subjected to injection molding by an injection molding machine, and the nylon-copper composite capable of preventing marine biofouling is obtained. The nylon-copper composite hasgood bioattachment resistance and good seawater corrosion resistance.