Abstract: A calculation model for economic back-pressure of direct air-cooling unit was set up based on the process mechanism, so as to analyze the influence of back pressure change on the generator terminal power and fan power consumption. Taking a 300 MW direct air-cooling unit as the object of study, the power generation benefit resulted from back pressure variation was calculated with the model at different loads, after which the variation tendency of back pressure with load was obtained. Results show that the economic back pressure of direct air-cooling unit increases with rising load; the power generation benefit obtained at economic back pressure varies with load; during low load operation, greatest power generation benefit will be produced when the back pressure parameters are optimized to make the unit work at the economic pressure.