A structure of distributed feedback (DFB) laser includes a grating layer having a phase-shift grating structure and a gratingless area. In addition, both side-surfaces of the DFB laser are coated with anti-reflection coating to improve SMSR and to obtain good slope efficiency (SE). The grating layer is divided by the phase-shift grating structure in a horizontal direction into a first grating area and a second grating area adjacent to a laser-out surface of the DFB laser. The phase-shift grating structure provides a phase-difference distance, such that a shift of phase exists between the micro-grating structures located within the first grating area and the other micro-grating structures located within the second grating area. The gratingless area located within the second grating area contains no micro-grating structure, and moreover, the gratingless area will not change the phase of the micro-grating structures located within the second grating area.