A simple and fast dispersion measurement method is proposed based on the fiber laser structure. The resonant cavity is composed of two mirrors, one composed of Sagnac ring and fiber coupler and the other composed of the fiber gratings with different central wavelengths. The fiber lasers are established with different independent wavelengths based on optical switch. Gauging the laser beat frequency, we can obtain the time delay of the optical fiber under different wavelengths and then can obtain the dispersion coefficient. The dispersion of a 500-m-long dispersion compensation fiber is tested by the proposed method. The results show that the method is feasible, easy to implement, and can realize the rapid measurement of the optical fiber dispersion. The method can provide a reference for the selection of fiber parameters such as the fiber type and length in the communication applications.