The invention discloses a method for converting equivalent grain size of a non-spherical bubble. The method comprises the following steps: calculating a coordinate of the center of mass for each bubble contour, establishing a plane right angle coordinate system with the center of mass as an origin of coordinates, separately calculating the numbers of pixels corresponding to radiuses in an X-axis direction and a Y-axis direction of the bubble contour and separately marking as rx, ry; separately selecting the rx and ry as the number of pixels rz corresponding to a radius in a Z-axis direction of a spatial right angle coordinate system of the bubble contour, calculating the volumes of two ellipsoids in accordance with an ellipsoid calculation formula, and solving a mean value of the volumes of the two ellipsoids as the volume of the non-spherical bubble; calculating the equivalent grain size of the non-spherical bubble by using a spherical volume formula. According to the invention, the method can implement 3D equivalent volume calculation of a 2D micro non-spherical bubble image, and can reduce errors in the course of equivalent conversion, increase precision of volume calculation, and further increase precision of equivalent spherical bubble grain size.