Sealed twin screw

The invention relates to a sealed twin screw, which is sequentially provided with at least four areas with different pressures along the moving direction of materials. The four areas include an area L1 (1), an area L2 (2), an area L3 (3) and an area L4 (4) and correspond to the pressure P1, the pressure P2, the pressure P3 and the pressure P4 respectively. Combination modes of the four different areas at least include at least one cycle of the L1 (1), the L2 (2) and the L3 (3), and connection of the L4 (4) after the cycle, or include the L1 (1), connection of at least one cycle of the L2 (2) and the L3 (3) after the L1 (1) and connection of the L4 (4) after the cycle. The sealed twin screw has the advantages that volatile components in melt are sealed, overflow of the volatile components during twin screw extrusion is avoided, the proportion of the components in the melt is kept within a certain range, the viscosity of the spinning melt can be maintained, and spinning can be smoothly performed.