The invention discloses a dual-channel laser detector of aerosol particles and a detection method. The detector is composed of a particles sample injection part and an optical sampling part which are connected, and a controlling and processing part composed of a power supply module (63), a gas control module (64), a detection module (65), a simulating module (66), a data module (67), an industrial control computer module (61) and a display (62) which is respectively electrically connected with a gas pressure sensor (17, 18), an airflow pump (07, 15), a laser (20), an ultraviolet laser (31), an avalanche diode (41) and a photoelectricity multiplication tube (50, 51). The method is that setting the working pressure ratio of the airflow pump, and according to the time difference and intensity of the signals twice output by the avalanche diode, acquiring the particle sizes of the aerosol particles, the distribution information of the particle spectrum and the information of biological active substance and riboflavin to generate corresponding images, then storing and transporting to the display to display. The invention can be used for real-time on-line detection of the aerosol particles in atmosphere.