The invention relates to a coaxial extruder and an
extrusion method thereof. The coaxial extruder comprises a die, a rectifying disc, an
extrusion device, a heater, a charging base and a power device, and is characterized in that the
extrusion device comprises a main screw
barrel, an outer screw and an inner screw; the two ends of the main screw
barrel are connected with the charging base and the die correspondingly, and the outer screw is arranged in the main screw
barrel and rotates; the inner screw is arranged in the outer screw and is in threaded connection with the rectifying disc; the inner screw and the outer screw are reverse in thread screwing direction, an additional thread is additionally arranged between main threads of the outer screw, the thread
pitch of the additional thread is larger than that of the main threads, and an additional thread groove is formed by the additional thread and the main threads; and the bottom, at the position of the additional thread groove, of the outer screw is provided with a melt channel. The length-
diameter ratio is greatly reduced, the strength of the outer screw is greatly improved, the number of heaters is reduced due to the shortened main screw barrel, and part of originally-emptied
waste heat is sufficiently utilized; the material cost and the occupied area are saved, and the fusion
raw material process time is shortened; the probability of decomposing of fusion materials due to overheating is reduced; and
power consumption is reduced.