Flour method is extensively used in the sprinkler droplet size measurement. The traditional calibration equation only considered the relationship between dried pellet mass and droplet diameter. The effects of droplet diameter, droplet impact angle and impact velocity on dried pellet mass were discussed through the orthogonal test. The results showed that droplet size and impact angle had significant influences on dried pellet mass while droplet impact velocity had little influence. A modified calibration equation considering two factors of droplet size and impact angle was established. The modified calibration equation had high calculation accuracy compared with the traditional one. The method of measuring sprinkler droplet using the modified calibration equation was presented with the application of the droplet dynamics-evaporation model.