The invention provides a tunable gain-control intermediate infrared pulse fiber laser and method for obtaining tunable gain-modulation intermediate infrared pulse fiber laser. The laser is composed of a first laser pumping source, a first dichroic mirror, a second dichroic mirror, a first convex lens, a double-cladding Er<3 +> fluoride fiber, a second convex lens, a plane blazed grating, and a second laser pumping source. And a 45-degree included angle is formed between the first dichroic mirror and the horizontal direction. According to the invention, a strict requirement on an active modulation device parameter or a passive modulation device parameter during the traditional intermediate infrared tunable pulse fiber laser generation process can be avoided. On the basis of dual-wavelength mixed cascade pumping, continuous laser and pulse laser are combined; and the gain-modulation intermediate infrared pulse fiber laser having the long wavelength is generated directly based on dual-wavelength mixed cascade connection, so that the high energy and high power of the output pulse fiber laser can be realized easily. Because of combination of the dual-wavelength mixed cascade method and the plane blazed grating, the tunable-intermediate-infrared-waveband-wavelength pulse fiber laser output can be realized easily.