Understanding the mechanisms responsible for product formation can provide critical insights into the design of effective reaction systems. In this paper, we have proposed the formation of the radical (O=C • -O-Cu) as initial step in CO2 reduction process and discussed various product formation pathways. We believe all products (except hydrogen gas) observed from Cu catalyst should be derived from a singular intermediate. The proposed radical (O=C • -O-Cu) provides clear and straightforward pathways for various product formation. Moreover, electrochemical CO conversion could also occur over Cu metal catalyst. It is possible to extend our assumption to the reduction of CO into other chemicals and fuels. The initial conversion step would form the radical ( • C=O-Cu), and subsequent radical reactions would lead to the formation of various products. We will discuss a fully detailed reaction process in future work.