A second sub-loop genetic optimization algorithm was proposed in order to improve the narrow particle distribution inversion by laser diffraction method,which suffers from inaccurate peak positioning and relatively big deviation in peak value measurement.Numerical simulation results show that the consistency between particle size distribution inversion curve by the second sub-loop genetic optimization algorithm and the actual particle size distribution curve has been significantly improved.In the range from 1 μm to 140 μm,peak positioning of the narrow particle distribution is accurate and the difference with the actual value is decreased to less than 1μm.Moreover,the precision of peak value is obviously increased and the relative error is reduced to about 10％.