The invention discloses a portable refractive index measuring device which comprises a light source, a focusing lens, an objective table, an imaging film, an eyepiece and a lightproof shell, the shell comprises a main body, a first telescopic shell and a second telescopic shell, the light source is mounted at the bottom in the main body, a first connecting port connected with the first telescopic shell is formed in one end, opposite to the light source, of the main body, the focusing lens and the objective table are mounted on the main body, and the light source, the focusing lens, the objective table and the connecting port are sequentially distributed; one end of the first telescopic shell is telescopically connected with the first connecting port, the other end of the first telescopic shell is provided with a second connecting port, an imaging film and an eyepiece are respectively arranged in two ends of the second telescopic shell, and one end of the second telescopic shell is telescopically connected with the second connecting port. The device can be reduced in size, is convenient to carry, can be used anytime and anywhere, is not affected by external light, and is accurate in measurement.