This paper proposes a method for simultaneous measurement of particle size and refractive index based on the orthogonal distribution difference of scattered light intensity of particles. The method uses the perpendicular/parallel components of the scattered light of the particles and the preset refractive index to calculate the particle size distribution through inversion with an improved Chahine algorithm. According to the obtained particle size distribution, the parallel/perpendicular components of the scattered light of the particles are calculated and compared with the measurement results for further calculation of the fitting residual. The possible refractive indexes are traversed and the fitting residual is driven to be infinitely small. The corresponding refractive index equals the refractive index of the particles and the corresponding particle size distribution equals the sample’s particle size distribution. The measurement results of ethylene-propylene copolymer standard particles, silicon carbide, and graphite samples show that the refractive indexes of non-absorbent particles and the imaginary part of the absorptive particles can be accurately measured by this method. An accurate particle size distribution can also be obtained with the preceding refractive indexes.