Abstract: In order to study the effect of CMT and MIG arc additive processes on the microstructure and properties of5356 aluminum alloy, the forming morphology, porosity, microstructure and mechanical properties of the two arc additive deposited specimens were compared and analyzed. The results show that the surface of CMT deposited specimen is uniform while the MIG deposited specimen has obvious collapse at the edge. The pores of the two deposited specimens are mainly near the fusion line between layers, while the MIG deposited specimen has more defects and larger sizes. The microstructure of the two deposited specimens is obviously different, the columnar crystal and fusion line of MIG deposited specimen are obvious,while the microstructure of the CMT deposited specimen is uniform equiaxial crystal. However there is obvious segregation in the CMT sample. The mechanical properties of MIG deposited specimen is anisotropic, while that of the CMT deposited specimen is isotropic.