The important role of alkali additives in the CO hydrogenation process is related to their high promotion effect. However, the wide application of alkali additives does not reflect a thorough understanding of the mechanism of their promotional abilities. Here, we have investigated the effect of potassium (K) on the isobutyl alcohol formation over CuLaZrO2 catalysts. It was found that K addition had a great effect on the C-C chain growth in spite of the occurrences of decreased surface area and increased CuO reduction temperature. Probe molecule experiments and in situ diffuse reflectance infrared Fourier transform spectroscopy revealed that K addition enhanced the formation of C-1 intermediates needed for isobutyl alcohol synthesis under high reaction temperature. Among the adsorbed species, bicarbonate species showed moderate adsorption intensity and benefitted from isobutyl alcohol synthesis. Meanwhile, K addition promoted the adsorption of linear CO, which was considered as another important intermediate for alcohols synthesis, thus accelerating the C-C chain growth.