Abstract: Lyocell fiber-reinforced poly(lactic acid) (PLA) composites were prepared by melting blending and injection molding in this work. The effects of silane coupling agent (KH550) and hexamethylenediisocyanate (HMDI) on the structure and properties of the composites were investigated by means of mechanical property test, DSC, Vicat softening temperature test, and SEM. It showed that interface modification of the HMDI was better than KH550. With the increasing content of HMDI, the mechanical properties of the composites increased firstly, then decreased. Compared with the composite without coupling agent, the composite containing 1 wt% coupling agent gave rise to a 5.1 ℃ higher Vicat softening temperature and better mechanical properties, with tensile strength, tensile modulus, flexural strength, flexural modulus, and notched impact strength being 57.1 %, 10.5 %, 32.3 %, 19.5 % and 23.7 % higher, respectively.