The invention provides an electrothermal-effect-based modulation type fiber-integrated Mach-Zehnder interferometer comprising a light source, single-mode optical fibers, optical fiber tapers, an asymmetric double-core optical fiber, an electric heating array, a power control system and a photoelectric detecting device. The light source is connected with one end of an asymmetric double-core opticalfiber by the first single-mode optical fiber and the first optical fiber taper; and the other end of the asymmetric double-core optical fiber is connected with the photoelectric detecting device by the second single-mode optical fiber and the second optical fiber taper. The asymmetric double-core optical fiber consists of a central core and a side core. The electric heating array is arranged at acoating at one side of the side core of the asymmetric double-core optical fiber and is connected with the power control system. The fiber-integrated Mach-Zehnder interferometer has advantages of simple and compact structure, high system stability, great convenience in manufacturing, low cost and great convenience in operation and has the broad application prospects in fields of optical fiber sensing, optical information detection, external environment monitoring and the like.