Utilizing renewable electricity energy to convert CO into fuels and chemicals, namely, CO electrocatalytic reduction reaction (CORR), is becoming increasingly significant yet challenged by low activity and selectivity. Recently, a growing number of studies have demonstrated that oxidized species can surprisingly survive on the catalyst surface under highly cathodic CORR conditions and play crucial roles in affecting the product selectivity. However, dynamic evolutions of the surface chemical state together with its real correlation to the product selectivity are still unclear, which is one of the most controversial topics for CORR. Herein, we particularly resurvey recent CORR researches that are all based on advanced in situ/operando methodologies, aiming to clearly reveal the realistic variations in surface chemical state under the working conditions. Then, recent progress in the regulation of the surface chemical state toward specific CORR products in current state-of-the-art catalysts with varying metal centers is systematically summarized, which shows an impressive relation between the dynamic chemical state and product profile. Next, we further highlight the developed strategies to regulate the surface chemical state in catalysts and discuss the debates over the effects of chemical state on product profile during CORR. Finally, on the basis of previous achievements, we present major challenges and some perspectives for the exploration of the imperative chemical state sensitivity to product profile during CORR.