The present invention provides a preparation method for gold nanoparticles based on functionalized ionic liquid. The method comprises synthesizing a functionalized ionic liquid, 3-(12-bromo-dodecyl)-1-(3-pyrrole propyl)-imidazole bromide, as a stabilizer for synthesizing gold nanoparticles, adjusting the concentration of the ionic liquid and the dosage of the reducing agent, thereby successfully preparing the icosahedral gold nanoparticles, and characterizing the morphology thereof by TEM, XRD and SEM. In the present invention, the method employed for preparing the stabilizer is simple, non-toxic, harmless and pollution-free, moreover the preparation of gold nanoparticles by aqueous phase has the advantages of mild conditions, short reaction time, simple operation, green and pollution-free, and belongs to the environment-friendly preparation.