Gold nanoparticles have been found to greatly enhance the polymerase chain reaction (PCR) specificity and yield in recent studies. However, the underlying mechanism is still unclear, though different hypotheses have already been proposed. In this study, a mass-action based model has been developed to investigate the effect of Au nanoparticles on the two-round PCR results. The great affinity of Au nanoparticles to the single-stranded DNA is taken into consideration. Each nanoparticle is treated as a bioreactor and/or a selector, around which, reaction equations are coupled to simulate the particle effect, and to investigate the key parameters that might influence such an effect. It is assumed that there exists a competing mechanism between the specific and nonspecific bindings, both in the solution and on the particle surface during the reactions. The numerical predictions accord well to the experimental results, and can be used to explain the Au nanoparticles’ effect on the enhancement of the PCR specificity and efficiency.