In this paper, an external high parallel magnetic field was superimposed into the codeposition process of Ni/nano-Al2O3 composites. It was found that the distribution of nanoparticles showed the network shape when superimposing a magnetic field, and the average size of the single network increased with increasing the current density. High concentration of nanoparticle could be obtained at low current density with a magnetic field, while a high current density was needed to realize that when without a magnetic field. The superimposed magnetic filed would improve the current efficiency. A possible mechanism on forming network shape was discussed.