Ultrasonic velocity measurement technology has become a research focus due to its non-invasive and pressure-loss-free advantages in addressing the measurement challenges of complex distorted flow fields, such as those in aero-engine intakes and industrial pipelines. This review introduces mainstream ultrasonic velocimetry methods, detailing the fundamental principles and calculation formulas of the transit-time method and the Doppler method. It focuses particularly on the ill-posed inverse problem inherent in ultrasonic velocity field reconstruction, providing an in-depth analysis of the mechanisms, strengths, and inherent ill-posedness of classical inversion algorithms including the least squares method, Tikhonov regularization, and truncated singular value decomposition (TSVD). The article summarizes key physical-signal joint processing strategies for mitigating significant ultrasonic beam drift and low signal-to-noise ratio (SNR). Looking ahead, it highlights the integration of physics-informed algorithms, multi-physical field coupling, and system-on-chip implementation as pivotal pathways for advancing the technology toward enhanced precision, adaptability, and miniaturization. This work serves as a reference for future breakthroughs and the engineering application of ultrasonic velocimetry technology.