MXenes with two-dimensional layered structure are widely used in the field of potassium ion supercapacitors because of their excellent electrical properties and adjustable surface functional groups, but their limited dual-capacitor storage capacity severely retards the application of MXenes materials in electrode materials. In this work, the strategy of “Lewis acid molten salt pre-etching + liquid phase etching + in situ hydrothermal recombination” was used to prepare the Ti₃C₂-based heterojunction with Ti₃C₂ as matrix and MnO₂ coated surface to improve the storage of potassium ions in electrode materials. The connection mode, electrical properties and the change of potassium adsorption law at Ti₃C₂-based heterojunction interfaces were studied by using the first principles calculation method based on density functional theory. The results show that the maximum adsorption capacity of potassium ions in the constructed Ti₃C₂-based heterojunction is about 3 times that of Ti₃C₂. The presence of Ti-O-H-O connecting channel increases the number of free electrons in MnO₂, causing Ti₃C₂-based heterojunction exhibiting excellent electrical properties. The electrochemical test results of the three-electrode system show that, at a current density of 1 A·g^-1, Ti₃C₂-based heterojunction can provide 431 F·g^-1 specific capacitance which is much higher than 128 F·g^-1 of bare Ti₃C₂. At a voltage sweep rate of 100 mV·s^-1, the contribution of pseudocapacitance is up to 89%. In addition, the Ti₃C₂-based heterojunction exhibits lower electrochemical impedance, which improves the potassium ion transport rate and electron transfer rate. Therefore, this study demonstrates that the electrochemical performance of Ti₃C₂ matrix can be improved by constructing Ti₃C₂-based heterojunction, and the corresponding energy storage mechanism can provide a theoretical basis for the design of other MXenes-based electrode materials.