According to the application requirements of multi-beam in multi-functional phased array system, a two-dimensional multi-beam forming method based on the combination of optical Blass matrix and a two-stage cascade structure is proposed, in which coherent beam forming method in optical domain is employed to form the first-stage beam in horizontal direction, and the incoherent beam forming method in optical domain is employed to form the second-stage beam in vertical direction, such that the two-dimensional beams can be realized. This architecture bears several advantages: on the one hand, the scale of optical phased array system can be increased from dozens to more than several hundreds units, and this can break the limitation on the scale of the optical array beamforming due to the small quantities of optical wavelengths. On the other hand, it can significantly reduce the number of optical beam forming chips, and the number of beam chips can be reduced from M 2 to (N+M) for the system with array number of N×N and beam number of M×M. Moreover, the structure of the multi-beam system can be drastically simplified by combining the photon integration technology, which is helpful to improve the integration degree and engineering realizability.