Abstract Cu can improve NO removal efficiency of char and CO in carbonation stage of calcium looping, but the mechanism of NO reduction by char and CO in the presence of Cu has been rarely reported. In this work, the density functional theory was utilized to investigate the effect of Cu on NO reduction by both char and CO in carbonation stage of calcium looping for CO2 capture. Density of state result proves that Cu decreases the possibility of char deactivation and retains stable promoting effect for NO reduction. Adsorption energies and structural parameters were used to determine adsorption sites of reactant molecules (CO, NO and O2) and Cu atom on the basic configuration of zigzag graphite structure with six benzene rings. Adsorption energies of reactant molecules on char surface in the presence of Cu follow the order: CO