Monitoring of raining conditions is of great importance to prevention and control of rainfall-triggered hazards.A novel rainfall rate measurement method based on videos is proposed in this paper.Firs t,raindrops are detected based on their intensity variation characteristics in the rain images.Secondly,in order to estimate the sizes of raindrops when their distances to the camera are unkown,focused and defocused factors are integrated into the photometry model o f raindrops imaging,and a discrimination method based on features of intensity differences and color tensor responses is constru cted.Then,sizes of focused raindrops are calculated by perspective imaging relations and an observed raindrop size distribution (RSD) c urve is built according to its definition in the field of meteorological science.Finally,in order to suppress noises in the observed rai ndrop size distribution,the observed RSD curve is fitted with the meteorological Gamma distribution model,and rainfall rate is calculate d based on the parameters of the model.In the experiments,the algorithm is tested under different rainy conditions,such as l ight rain,moderate rain and heavy rain. Measurement results using the proposed algorithm are compared with the data reco rded by a pluviometer.It is shown that the results are consistent very well.