▎ 摘　　要

We study the electron transport through the graphene pnp junction under a magnetic field and show that mode mixing plays an essential role. By using the nonequilibrium Green's function method, the space distribution of the scattering state for a specific incident mode as well the elements of the transmission and reflection coefficient matrices are investigated. All elements of the transmission (reflection) coefficient matrices are very different for a perfect pnp junction, but they are the same at a disordered junction due to the mode mixing. The space distribution of the scattering state for the different incident modes also exhibits similar behaviors, i.e., that they distinctly differ from each other in the perfect junction but are almost the same in the disordered junction. For a unipolar junction, when the mode number in the center region is less than that in the left and right regions, the fluctuations of the total transmission and reflection coefficients are zero, although each element has a large fluctuation. These results clearly indicate the occurrence of perfect mode mixing and play an essential role in a graphene pnp junction transport.