The invention discloses a method for testing droplets in smoke, which comprises following steps: firstly, setting a droplets sampling system, secondly, testing and calculating smoke flowing speed through an L-shape Pitot tube (11), thirdly, adjusting airflow controlling valve (9a) which is on a vacuum pump of the droplets sampling system according to the tested smoke flowing speed. Droplets concentrations can be calculated according to the quality of the droplets which are collected by a droplets collecting device. The invention adopts a method of constant velocity aspirating smoke, the droplets in the smoke are collected by the droplets collecting device, droplet quality can be obtained through weighing the weight of the droplets collecting device before and after collecting, and furthermore the droplets concentrations can be obtained through formulas. Compared with a traditional method, the method needs no precise equipment tests as atomic absorption spectrometry, thereby testing data is minimized, the operation is easier, and testing results are more accurate.