A one-step strategy of preparing hierarchical porous poly (formaldehyde-melamine) monoliths (PFM) with high specific surface area was proposed. Based on the high internal phase emulsion (HIPE) template, the removal of dispersed phase (liquid paraffins) and the reaction-induced phase separation in continuous phase (the solution of parafomaldehyde and melamine) could generate the macropores, mesopores and micropores in PFM simultaneously. As a result, the highest specific surface areas of the prepared PFM could reach 210 m(2)/g, which was obviously higher than that of traditional polyHIPE. The effect of the constitution of the continuous phase of HIPE on the macroporous morphologies, specific surface areas, and micropore volume of PFM were investigated in detail. Moreover, the formation mechanism of micropores and mesopores by reaction-induced phase separation was proposed. Finally, the obtained PFM was applied as CO2 absorbent and the adsorption properties were studied.