It has been proved by experimental results that the ohmic contact property of silicon carbide can be improved by using some specific nanometer metal particles. In this paper, authors have constructed a quantum tunneling models to explain the experimental results. The influences of parameters on the ohmic contact characteristics have been calculated based on the models. The values show that the tunneling effect can be observed by adding nanometer particles. The tunneling probability has been increased. Moreover, with the existence of nanometer particles, pinning of Fermi level has been conquered. So, it is an effective method by using specific nanometer metal particles to improve the characteristic of P-type silicon carbide ohmic contact.