As one of the important components of the supercapacitor, electrode material has a significant influence on the electrochemical performance of the device. In this study, Ni2(NO3)2(OH)2 · 2H2O/(Co(NH3)5(N3))(N3)2 (NC) composite material was prepared by the microwave-assisted method. The effects of Al(NO3)3 contents on the morphology and structure of the composites were studied by scanning electron microscopy, X-ray diffraction, Raman spectrum, and laser particle size distribution analyzer. The capacitive properties of the composite were analyzed by cyclic voltammetry, constant current charge and discharge, and electrochemical impedance spectroscopy measurements. The results show that the Al(NO3)3 has a significant effect on the morphology and capacitance of NC. When the contents of Al(NO3)3 are 0, 5, 10, 15, and 20 wt%, the discharge capacities of NC, NCA-5, NCA-10, NCA-15, and NCA-20 samples obtained under 1 A/g current density are 1674, 1759, 2645, 1098, and 1321 F/g, respectively. At higher current densities of 4, 7, and 10 A/g, the discharge specific capacities reached 1350, 1064, and 894 F/g, indicating that the NCA-10 composite is a promising electrode material for supercapacitors.