Particulate matter particle size measuring system and mass spectrometer

The invention relates to a mass spectrometer of a particulate matter particle size measuring system. The particulate matter particle size measuring system comprises a laser generating mechanism, a vacuum cavity and a scattered light collecting mechanism, wherein the laser generating mechanism is used for generating two beams of parallel laser and guiding the laser into the vacuum cavity. In the vacuum cavity, particles to be detected fly through the two beams of parallel laser and generate scattered light. The scattered light collecting mechanism adopts a front end collecting assembly, an optical fiber assembly and a photoelectric detection assembly, so the distance between two diameter measuring laser beams can be effectively shortened, the overshoot phenomenon occurring when particles fly over the two laser beams is reduced, and the accuracy of particulate matter measurement is improved. And by reducing the distance between the two diameter measuring laser beams, the influence causedby particle beam diverge