The alignment accuracy of the two-mirror telescopes is a key link to ensure the imaging quality of the system. One of the currently used alignment methods is to use the coma of the on-axis field of view(FOV)as a reference, which cannot effectively guarantee the imaging quality of the system’s entire FOV. Based on the vector wave aberration theory, the aberration field characteristics of the two-mirror telescopes is analyzed in this paper. According to the characteristics of the coma field and astigmatism field of the misalignment system, an alignment method based on the astigmatism of symmetric off-axis FOV is proposed. According to the theoretical analysis results, taking an R-C two-mirror telescope as an example, the alignment method using on-axis field coma and the off-axis symmetric field astigmatism proposed in this article were analyzed under a given initial misalignment state. A systematic simulation alignment experiment was carried out based on the method in the paper. The results showed that when the on-axis coma is zero after moving the secondary mirror, the astigmatism of the full FOV was 1.02λ, and the system did not reach the optimal alignment state. However, after the alignment using the astigmatism of off-axis symmetrical FOVs, the average astigmatism of the system’s entire FOV is 0.46λ, which is basically consistent with the theoretical design value, indicating that the method proposed in this article is effectively completed the alignment of a two-mirror telescope.