The invention discloses Mach-Zehnder interferometer integrated in an optical fiber and the manufacture method thereof; two sections of single core optical fibers are respectively provided on two sides Mach-Zehnder interferometer, and one section of two-core optical fiber in the middle of Mach-Zehnder interferometer are welded and tapered, and hence the Mach-Zehnder interferometer is formed; the Mach-Zehnder interferometer comprises a single mode single core input optical fiber (1), a light splitting taper-shaped coupling area (2), a single mode double-core optical fiber (3), a light composite taper-shaped coupling area (4) and a single mode single core output optical fiber (5); the single mode single core input optical fiber (1), the single mode single core output optical fiber (5) and the single mode double-core optical fiber (3) are connected with each other through the light splitting taper-shaped coupling area (2) and the light composite taper-shaped coupling area (4). The invention has the advantages that interferometer has great stability, avoids the variation positions of all moveable parts because of assembly, fixing and regulation, reduces the volume of the interferometer and makes the system more simple and more compact; as the optical path differences of two interference arms positioned in the double-core optical fiber are very small, the invention doesn't need huge mutual coherence of light source and can implement auto-compensation of optical paths of the two interference arms.