Abstract: Waste paper fiber/polylactic acid composite was prepared by hot-press molding method. The micromorphology, mechanical properties, thermal stability and water absorption property of the composite before and after adding KH550 were studied. The results show that after adding KH550, the tensile fracture of the waste paper fiber/polylactic acid composite was smoother, and the interfacial compatibility between waste paper fiber and polylactic acid was greatly improved. When KH550 solution with 5% mass fraction was added, the tensile strength and flexural strength of the waste paper fiber/polylactic acid composite added with KH550 increased by 11.2% and 8.4% respectively compared with those without KH550. When KH550 solution with 5% mass fraction was added, the water absorption of waste paper fiber/polylactic acid composite decreased. The addition of KH550 had little effect on the thermal stability of the composite.