The invention relates to a method for rapidly preparing a water-soluble quantum dot by an ultrasonic spraying method with continuous production, which comprises the following steps that: cadmium ions or zinc ions and hydrogen (or selenide) telluride or sodium hydrogen telluride (or selenide) react to obtain a precursor solution of cadmium (zinc) telluride (selenide) through the complexation of a mercapto compound. An ultrasonic atomizer is used to atomize the precursor solution to form fogdrops of the precursor solution, and the fogdrops flow through a device with constant temperature to react to obtain the water-soluble quantum dot. The method has the advantages of high speed and continuous quantum dot production, the prepared quantum dot has high fluorescence quantum yield (between 20 and 50 percent), and good monochromaticity of luminescence (the peak width at half height of a fluorescence spectrum within the range of visible light is between 30 and 40nm), and the size of nano-particles can be easily controlled by changing the temperature and flow rate, thereby realizing the adjustment to luminescence peak positions (between 400 and 700nm).