The invention relates to a laser particle size analyzer employing a combination of forward and backward Fourier light paths. The laser particle size analyzer comprises a laser device, a lens, a samplecell and photodetectors, wherein the parallel light of the laser device passes through the lens and becomes convergent light that enters the sample cell; a plurality of the photodetectors are mountedrespectively in front of the sample cell, beside the sample cell and behind the lens; the photodetectors are composed of forward detectors and backward detectors; the forward detectors employ the form of a backward Fourier light path and are cooperated with the obliquely placed sample cell; and the backward detectors are arranged on the rear cambered surface of the lens. The laser particle size analyzer of the invention overcomes the defects of a single optical path form of conventional laser particle size analyzers and makes up shortcomings of the laser particle size analyzer by adopting thestrong points of conventional laser particle size analyzers; and since the sample cell is obliquely placed in the forward Fourier light path, breakthroughs are made to the limitation of total reflection angles, and a larger forward scattering angle receiving scope is broadened.