The present invention discloses a heat adhesive biodegradable bicomponent fiber comprising a polylactic-acid-based low melting component and a high melting component, wherein the low melting component constitutes the sheath of the fiber, and the high melting component constitutes the core of the fiber. The material of the low melting component comprises unmodified polylactic acid or a blending with unmodified polylactic acid and modified polylactic acid. The modified polylactic acid is modified by blending unsaturated dicarboxylic acid, unsaturated anhydride or their derivatives with polylactic acid. The bicomponent fiber provided in this invention is biodegradable, environmentally benign and with excellent bonding performance to polylactic acid fibers, chemical fibers and cellulose fibers.