The invention discloses a continuous steam explosion device for plant fibers. The continuous steam explosion device comprises a barrel, a transmission mechanism and a driving mechanism which are sequentially connected, a feed inlet and a discharge outlet are arranged on the barrel, three screws located on the same horizontal plane are disposed in the barrel, the adjacent screws are radially meshed mutually, the cross sectional area of the end, which is close to the feed inlet, of each screw is larger than that of the end, which is close to the discharge outlet, of the screw, and the driving mechanism is connected with the screws and drives each two adjacent screws to rotate in opposite directions. The continuous steam explosion device can realize continuous steam explosion for materials, and has the advantages of simple structure, low manufacturing cost, fine steam explosion effect and high yield.