Abbe number is an important fundamental parameter in the field of optical design. Compared to solids, data of liquid Abbe number is relatively scarce. With the development of liquid optical systems, accurate measurement of liquid Abbe number is becoming increasingly important. The commonly used methods for measuring the Abbe number of transparent liquids have drawbacks such as cumbersome operation, low measurement efficiency, and unsuitable for measuring toxic and volatile liquids. Therefore, a method for measuring the Abbe number of transparent liquids based on the defocusing width of a composite liquid-core cylindrical lens is proposed. During the experiment, it is only need to rotate the coaxial filter wheel to replace the filters for red, yellow, and cyan light, and then CCD can capture the defocused images under three different light sources quickly. Based on the good linear relationship between the defocused image width and the refractive index of the liquid, the refractive index of the transparent liquid at three wavelengths can be obtained, and the Abbe number can be calculated. This method combines the advantages of simple experimental setup, easy operation, and fast measurement, which can be used to quickly expand the basic data of transparent liquids Abbe number.