The present disclosure relates to a particle counting method and system. The particle counting method, comprises: obtaining distances between positions closest to a centers of a light channel in paths along which particles pass through the light channel and the centers of the light channel; according to an optical density distribution of the light channel, compensating amplitudes of the pulse signals of the particles when passing through the positions closest to the centers of the light channel in the path along which the particles pass through the light channel such that the compensated amplitudes of the pulse signals of the particles are equal to amplitudes of pulse signals of the particles with the same particle diameters when passing through the centers of the light channel; screening and counting the particles according to the compensated amplitudes of the pulse signals to realize counting of particles with respective particle sizes.