Good conductivity is the key to ensuring high electrochemical performance, and the uniformity of theactive material directly affects the electrical conductivity. This paper proposes a novel modified stepwisein situ polymerization method to prepare composite materials, and then uses the K/S value method tocharacterize the uniformity of polyaniline distribution. Specifically, the study presents a papermakingwet-lay technique to prepare a carbonfiber paper substrate (CP) that is light-weight,flexible, andfoldable while also having low internal resistance and high porosity. The g-MnO2 is wrapped with PANI toform a core–shell structure, and a modified stepwise in situ polymerization method is adopted to depositthe core–shell structure uniformly on the CP substrate by physical adsorption. This process yields aflexible electrode material for supercapacitors, called g-MnO2-PANI-CP electrode. Results show thatthe g-MnO2-PANI-CP electrode has a high specific capacitance of 642.5 F g 1 at a current density of 1A g 1, and also has a high energy density of 114.2 Wh kg 1 at a power density of 798.6 W kg 1. In addition,the electrode retains 81.3% of the initial capacitance after 5000 cycles, demonstrating high cyclingperformance.