For measurements on particle size, an improved reverse Fourier laser measurement system (RFS) which based on disadvantage traditional Fourier system (FS) is presented. In the experimental parts, the results show that the increase in lower limit of particle size measurement by increasing the distance of scattering volume and lens can expand the range of particle size measurement. In addition, the different particle size measurement results and theoretical calculation results are compared. The experimental evidence and simulation results show that, this method is especially suitable for measuring small particles.