The invention relates to a fermentation air preprocessing system applying a plate-fin heat exchanging technology. The fermentation air preprocessing system comprises a horizontal air cooler, a horizontal gas-liquid separator and a horizontal air heater, wherein a plate-fin heat exchanging assembly is arranged in the air heater; the air cooler and the gas-liquid separator are arranged in a horizontal housing in a combination manner; high-temperature air entering the fermentation air preprocessing system is divided into two ways; a main pipeline is connected with the air heater; a branch pipeline is connected with the housing; the right side of the housing is connected with a cold flow inlet of the air heater; a thermal flow outlet in the air heater is connected with an air inlet interface through a by-pass pipeline; an independent plate fin thermal flow channel and a plate fin cold flow channel are arranged in the air heater; a switching valve is arranged on the main pipeline; and an automatic adjustable valve is arranged on the branch pipeline. The fermentation air preprocessing system disclosed by the invention is reasonable in structural design, high-efficiency, and energy-saving; the air resistance is low to be within 5kPa, the heat transfer coefficient is increased, the system is succinct and reliable, and besides, the manufacturing cost and operating cost are reduced, so that the air quality at the outlet of the system is improved, and the stable production through fermentation is promoted.