Embodiments of the invention disclose a coupler and an optical waveguide chip using the same, and relate to the field of optical fiber communication. The insertion loss during coupling of optical waveguide signals at the two sides of the coupler can be reduced. The coupler is used for connecting a first optical waveguide and a second optical waveguide, and comprises an entity area and a first waveguide grating. A first end of the entity area is coupled to the first optical waveguide, a second end of the entity area is coupled to a second end of the first optical waveguide, and a first end of the first optical waveguide is coupled to the second optical waveguide, wherein the size of the first end of the entity area matches the end face size of the first optical waveguide, the size of the second end of the entity area matches the end face size of the second end of the first optical waveguide, and the size of the first end of the first optical waveguide matches the end face size of the second optical waveguide. The width of the entity area changes linearly and gradually. The coupler and the optical waveguide chip disclosed by the embodiments of the invention are applied to optical fiber communication.