Transition metal dichalcogenides (TMDs) possess several advantages, such as high conductivity, stable structure, and low cost, making them promising catalysts for carbon dioxide electroreduction. However, the high overpotential and the desorption characteristics of the reaction products during the reduction of carbon dioxide present significant challenges in the field of catalysis. In this study, we have further enhanced the catalytic activity of the original WS2 structure by constructing a heterojunction. We systematically investigate the catalytic activity of MoS2/WS2 heterojunctions supported by transition metals using density functional theory (DFT) calculations. The findings of this study are as follows: (1) the unique multiphase structure enhances the catalytic performance for CO2 reduction. (2) After constructing the MoS2/WS2 heterojunction, the electronic properties and conductivity of the heterojunction can be significantly enhanced, thereby facilitating the catalytic reduction of carbon dioxide. The Cu loading on the Cu@MoS2/WS2 heterojunction significantly reduces the overpotential, with a very low limit potential of -0.58 V. The adsorption behavior of CO on the Cu@MoS2/WS2 heterojunction was evaluated using adsorption energy, desorption energy, and density of states (DOS). The appropriate interaction between CO and Cu@ MoS2/WS2 promotes the reduction of CO2 to CO and facilitates smooth desorption of CO, demonstrating a strong catalytic effect on the CO2 reduction reaction (CO2RR). Therefore, it can be seen that Cu@MoS2/WS2 may be considered as potential single-atom catalysts (SACs) for CO2 reduction electrocatalysts. Finally, it is hoped that our results will provide theoretical support for the development of efficient CO2 reduction catalysts.