The invention discloses a method for measuring the refractive index of droplets based on digital coaxial holographic measurement. The method includes the following steps that: a droplet hologram is recorded; the particle diameter d of droplets and a droplet center position are obtained according to the recorded droplet hologram; the brightness distribution map of an x-z plane is drawn according tothe droplet hologram, the focus position of the droplets is positioned, so that a droplet focus position and the focal length f of the droplets are obtained; and the refractive index of the droplet is calculated according to relations between a refractive index n0 and the focal length f and particle diameter d of the droplets, and an air refractive index ni. The invention also provides a coaxialholographic measuring device. The device comprises a signal transmitting unit, a signal receiving unit, and a signal processing unit; the signal transmitting unit comprises a continuous laser for generating laser, and an optical path adjusting section; and the signal receiving unit comprises a microscope objective lens and a CCD camera. With the method and device provided by the invention adopted,the simultaneous measurement of parameters such as a dynamic droplet size and a refractive index is realized, and therefore, a droplet dynamics process is analyzed, and the on-line measurement of processes such as spray cooling and droplet combustion can be realized.