With the continuous development of telemetry technology, there higher higher requirements for phased array beamfor-ming capabilities and anti-interference capabilities. Based on the iterative Fourier algorithm, this paper proposes a new two-stage optimization algorithm to solve the spaceborne phased array beamforming problem. In the first stage, the iterative Fourier algorithm is improved by adding virtual array elements with zero excitation to supplement the array and increasing dynamic range constraints of the array element excitation, so that it can be used to achieve beamforming and low sidelobe requirements. In the second stage, the excitation with low sidelobe characteristics obtained in the previous stage is used as the constraint vector of the new beamforming algorithm, so as to improve the anti-interference performance of the phased array without changing the original response as much as possible. The experimental results show that the proposed two-stage optimization method can reduce the sidelobe level while beamforming, enhance the anti-interference performance of the array, and has high computational efficiency.