The invention relates to a plant fiber impregnation device and method applicable to natural plant fiber impregnation molten resin. The plant fiber impregnation device comprises a melting and impregnation die (1) and a cooling and rolling device (2), wherein the melting and impregnation die (1) comprises a die cavity, a feed inlet (4) and 4-8 and impregnation roller pairs located in the die cavity, each impregnation roller pair comprises an upper impregnation roller (6), a lower impregnation roller (5) and an impregnation roller spring (7), and the impregnation roller spring (7) applies certain elastic pressure to the upper impregnation roller (6) to allow certain pressure to exist between the upper impregnation roller (6) and the lower impregnation roller (5); the cooling and rolling device (2) comprises 2-4 compression roller pairs, each compression roller pair comprises an upper compression roller (9), a lower compression roller (10) and a compression roller spring (8), and the compression roller spring (8) applies certain elastic pressure to the upper compression roller (9) to allow certain pressure to exist between the upper compression roller (9) and the lower compression roller (10). The plant fiber impregnation device has the advantages that natural plant fibers are carded into strips and pass the plant fiber impregnation device, and natural long fiber reinforced thermoplastic polymer pre-impregnated materials.