Analysis of viable organisms in discharged ballast water including organisms greater than or equal to 10 micrometres and less than 50 micrometres in minimum dimension, organisms greater than or equal to 50 micrometres in minimum dimension, Escherichia Coli, Intestinal Enterococci and Vibrio cholerae is required in detail by D-2 standard of the International Convention for the Control and Management of Ship's Ballast Water and Sediments. Now a lot of research on ballast water treatment have been done in the world, but some problems still exist in the detection of living organisms, especially in fast detection methods. Several methods including microscopy, flow cytometry, microfluidic chip, molecular biology method, MPN method and plate method are introduced, including their principle, characteristic and limitation in fast detection of ballast water. Based on the characteristics of fast, accuracy, small consumption of sample and high automation, Flow cytometry is the most suitable method for fast detection of ballast water. The convention has no detailed rules on the number of cysts in discharged ballast water, but cysts have worse potential destructiveness to ecosystem, so more research on cyst should be carried out.