This study proposes a method to measure the backward scattered signals from particles illuminated by Gaussian beams. Micro-glass beads suspended in the fluid are measured, and the measured pulse waveforms are analyzed. Results reveal that the signal profile fits the Gaussian profile; the height of the Gaussian profile is approximately linear to the particle diameter. The standard glass beads with diameter of 19.2 μm are used to acquire signals under different number concentrations in real time, and the dependence of the pulse number on the particle concentration is obtained. Experimental results also confirm that the proposed method can measure both the particle size and concentration, thereby providing a basis for the measurement in the amplifier cavity of a laser system in the future.