CO2 electrolysis system (CES), as a type of carbon capture, utilization, and storage, has significant potential for achieving carbon neutrality. By utilizing surplus renewable energy, CES can convert CO2 into valuable electrochemical products. This paper studies the advantages brought by the application of CES to the green economic operation of multi-energy system. Firstly, a linear model based on the CES's operation data is developed to characterize its dynamic behaviour. In addition, a two-stage stochastic programming model for the operation of CES within multi-energy system is studied. Finally, a creative optimal-operation-based end-of-life net present value (OENPV) is proposed to assess the long-term investment of CES. The results of the cases in different seasons and electrochemical products show that the application of CES not only brings significant carbon reduction to the multi-energy system, but also alleviates the curtailment of renewable energy. Additionally, according to the OENPV analysis outcome, the production of formic acid gives the system the shortest return on investment, which is the fourth year of the 20-year assessment cycle.