Photocatalytic CO2 reduction to fuels and valuable chemicals by two-dimensional (2D) covalent organic framework nanosheets (CONs) is gathering much attention. However, it is still a challenge to improve photocatalytic performance. Herein, cobalt and nickel coordinated guanidinium-based 2D covalent organic framework nanosheets were synthesized by the condensation reaction between triformylphloroglucinol (TP) and triaminoguanidine (TG). In photocatalytic CO2 reduction, CO2 could be converted to CO effectively by using the prepared cobalt and nickel coordinated 2D CONs as photocatalyst. In particular, cobalt coordinated 2D guanidinium-based CONs (denoted as Co-TPTGCl) was the most effective, CO and H2 production rate reached up to 14641 μmol mg-1 h-1 and 7968 μmol mg-1 h-1, respectively. Compared with Ni-based catalyst, Co-based catalysts exhibited better catalytic performance in the photocatalytic CO2 reduction. From the characterizations of fluorescence spectroscopy and CO2 absorption-desorption isotherm, Co-TPTGCl 2D CONs owns longer fluorescence lifetimes and better absorption capacity of CO2.