This paper proposes a laser far-field focal spot measurement method based on multistep phase retrieval. The effectiveness of the method is verified through theoretical simulation and experiments. The theoretical simulation results show that the near-field complex amplitude and far-field focal spot of lasers are effectively retrieved. Additionally, the PIB curves of the theoretical and retrieved focal spots are coincident. Moreover, the experimental results show that the profile of the retrieved phase is consistent with that of the theoretical phase loaded using SLM. Therefore, the retrieved and theoretical focal spots have the same distribution of the main lobe. However, there is a small difference in the side lobes because the optical components introduce small aberrations, and the surfaces of these optical components will interfere with each other. The side lobe information of focal spots using the long-focal-length lens imaging method is lost because of the limited dynamic response range in CCD. Therefore, the proposed method has higher precision of laser far-field focal spot than the traditional long-focal-length lens imaging method. The results show that the proposed method can provide a technical means for the high-precision measurement of laser far-field focal spots.