The invention discloses a bubble particle size back calculation method. The method includes the steps that resolution ratio plates of stripe groups with different width grades are immersed in water; the stripe groups on the resolution ratio plates are shot, and target stripe images are formed; the number of pixels corresponding to widths of target stripes is calculated out according to the target stripe images; for the stripe group with each width grade, the correspondence relation between the widths of the target stripes and the number of pixels is established, and a relation model is formed; the number of pixels corresponding to the particle size of the bubble to be measured is calculated; the particle size of the bubble is calculated out according to the relation model. A mode combining image calibration and back calculation is adopted for the bubble particle size back calculation method to generate the physical size of the bubble particle size, and the method is high in precision, good in real-time performance, capable of achieving in-situ and real-time measurement of bubble physical parameters, suitable for being widely applied to the fields of scientific research, teaching, seawater monitoring and the like and particularly suitable for conducting in-situ detection on seawater bubble.