The invention relates to the technical field of microchemical equipment, and aims at providing a microchannel reactor. The microchannel reactor comprises a casing, a first communication mechanism, a second communication mechanism and a plurality of reaction tubes, wherein the plurality of reaction tubes are connected onto the casing and penetrate through a heat exchange cavity of the casing; a first communication channel is arranged on the first communication mechanism; the first communication channel corresponds to a first opening of the reaction tube; a second communication channel is arranged on the second communication mechanism; the second communication channel corresponds to a second opening of the reaction tube. Through the first communication channel and the second communication channel, at least two reaction tubes in the plurality of reaction tubes are selectively to be sequentially communicated, so that a reaction channel for reaction materials to flow is formed; on the premise of not changing the casing length, the length of the reaction channel is prolonged; the space is saved; the equipment cost is reduced; further, the retention time of reaction media is prolonged.