A method of holographic cross-connection is proposed for an Optical Ising machine system. The designed optical Ising machine based on multi-core fiber laser is introduced, including the theory of computation, history of optical computing, the concept of Ising model, the significance of optical Ising machine, the method to achieve Ising machine optically. The cross-connection part is based on computer-generated holograms (CGH), which is produced by Gerchburg-Saxton algorithm. The coupling coefficient between two channels as well as the phase change are controlled by CGHs. The design of holograms is discussed. The instrument used to display holograms is phase-only liquid crystal spatial light modulator (SLM) from HOLOEYE company. The optical system needed in this project, such as collimation lens and relay lens, is designed using Zemax. The system is first evaluated in Zemax simulation, and then constructed experimentally. The results show that we can control amplitude and phase of the reinjection beam at Multi-core fiber. Further experiment should be done to conclude that the control of the cross coupling between channels is achieved by displaying different holograms.