With the development of the times, the demand for rapid detection of trace toxic and harmful components and circulating tumor cells is increasing and it is urgent to develop portable specialized detection instruments. Since it is difficult to directly measure the sample material in the trace amount detection, the method of high-enrichment of the trace substance based on the ion concentration polarization principle can make the trace substance easy to be determined. In this paper, a novel micro-nanofuidic preconcentrator with Koch fractal nanochannel surface is proposed. By coupling the Poisson-Nernst-Planck equation and the Navier-Stokes equation, the influence of Koch fractal parameters on ion enrichment was studied by numerical simulation. The results show that increasing the unit length L, increasing fractal time n, using the unstraggered structure and increasing the fractal angle θ can significantly increase the ion enrichment ratio. In addition, we found that the above means can reduce the fluid flow velocity in the nanochannel and thus reduce the negative influence of electroosmotic flow on ion enrichment. This work provides a theoretical basis for the design of trace detection instruments based on micro-nanofluidic platform.