One-step synthesis of dimethoxymethane (DMM) via selective oxidation of methanol under nanocarbon catalysis is a green and sustainable but challenging chemical process. In the present study, a series of phosphorus-modified onion-like carbon (POLC) was prepared, and they have shown high activity in methanol conversion to DMM reaction. The proposed POLC catalysts exhibit two kinds of P-containing species, and C–P species is considered as the key factor to ensure the high DMM formation rate via linking the chemical structure to the catalytic performance of the catalysts. A temperature-programmed desorption experiment of the intermediate product formaldehyde (FA) reveals that the physical–chemical nature behind the promotion effect of C–P species enhances the adsorption ability of the catalyst to FA, thereby ensuring the subsequent condensation reactions to form DMM under high selectivity.