In order to implement the large beam pointing range and the fine step adjustment of an optical beamforming network (OBFN), a method of optical dispersion-based optical true time delay (OTTD) was adopted. The path switching of N-way high dispersion fiber was realized by the optical switch, and thus the equally large-step delay difference was realized, then the beam pointing with a large range and a stride adjustment was realized. By tuning the dispersion coefficient of the linear chirped fiber Bragg grating (LCFBG), the equally small-step delay difference was realized, and then beam pointing with a small range and a small-step adjustment was realized. The theoretical analysis and simulation verification of the above method were carried out, and a beam pointing angle range of -73.74°~+73.74° and a switching step of 0.458° was obtained. The result shows that the large beam pointing range and the fine step adjustment of the OBFN were realized based on optical dispersion, which is helpful to improve the system designing of phased-array antenna.