1. A smoke detection method based on video processing comprising: capturing images in a monitored area by an image capturing device; segmenting moving regions from the captured images by a computing device, each moving region comprising a plurality of pixels; extracting a plurality of smoke pixels from the plurality of pixels in the moving regions according to a first rule by the computing device; and determining whether the plurality of smoke pixels forms real smoke by the computing device according to a disorderness and a growth-rate of the plurality of smoke pixels, comprising: determining the plurality of smoke pixels as real smoke by the computing device when a number of times which an average growth-rate of the smoke pixels is greater than a threshold of growth-rate exceeds a predetermined value within a time duration, wherein the average growth-rate of the smoke pixels is an average of the growth-rates of the smoke pixels, and each growth-rate of the smoke pixels denotes a difference between the numbers of smoke pixels at a first time slice and a second time slice divided by a time difference between the first time slice and the second time slice.