The invention discloses a double-beam aerosol particle concentration detection device. The double-beam aerosol particle concentration detection device comprises a light source, a flow channel space for passing of aerosol, a gathering unit for gathering light emitted by the light source and then radiating the light into the flow channel space, and a collection unit for collecting scattered light signals, wherein the gathering unit comprises a collimating lens for converting the light emitted by the light source into parallel light, a semi-transmitting mirror for forming the parallel light intoa first light beam and a second light beam, a reflecting mirror for adjusting the first light beam and the second light beam to be parallel, and a first lens for gathering the first light beam and thesecond light beam to a light spot focus point; and the light spot focus point is located in the flow channel space. According to the double-beam aerosol particle concentration detection device, no light blocking plate needs to be used; extra reflection light is not generated; meanwhile, scattering light with a small scattering angle can be collected; the double-beam aerosol particle concentrationdetection device is capable of avoiding influence of stray light signals and collecting effective scattering light signals as many as possible, so that the accuracy of detection can be improved.