A finite difference scheme to control divergence error of electromagnetic field is proposed to study magnetic reconnection. With this simple numerical scheme, divergence errors of electromagnetic field are limited in the magnitude of rounding error. Our results are in good agreement with that in GEM. Influences of c/u_A and m_i/m_e on magnetic reconnection are also studied. It indicated that with the increase of c/u_A, net charge densities decrease while reconnection rate remains almost unchanged. The increase of m_i/m_e could lead to current sheet thinning and acceleration of reconnection.