In order to enhance the detection sensitivity of aerosol particle spectrometers, a method that two photodetectors were used to separately detect the side-scattered light of small particles and the forward-scattered light of large particles was employed. A miniaturized high-sensitivity aerosol particle spectrometer based on light scattering was designed and developed. Polystyrene standard microspheres were used to test the signal response of the particle spectrometer. Comparative observations were conducted with similar foreign products for 24 h, showing good concentration correlation and consistent trend between the two instruments during the test period. The results indicate that, the developed aerosol particle spectrometer has a minimum resolution particle size interval of 20 nm, and it is characterized by small size and light weight. This study provides important reference for aerosol detection using small unmanned aerial vehicles.