The invention provides a reaction system for preparing butyraldehyde by propylene carbonylation, comprising: a reactor; a side wall of the reactor is sequentially provided with a catalyst inlet, a propylene inlet and a synthesis gas inlet from top to bottom; the bottom of the reactor is provided with a solvent inlet; two micro-interface generators are arranged inside of the reactor from top to bottom, and the micro-interface generator located at a top end is connected to the propylene inlet to break the propylene gas into micron-scale micro-bubbles; the micro-interface generator located at a bottom is connected to the synthesis gas inlet for breaking the synthesis gas into micron-scale micro-bubbles; the outlets of the two micro-interface generators are opposite, and the outlets are connected with a gas distributor for evenly distributing raw materials. The reaction system of the present invention has low energy consumption, low cost, high safety, low reaction temperature and low reaction pressure, few side reactions and high yield of n-butyraldehyde, which is worthy of wide popularization and application.