Abstract: The existing magnetic flux leakage (MFL) testing technique is insufficient for effectively identifying cracks in girth welds of oil and gas pipelines. This paper presents a study on the application potential and bottlenecks of magneto-optical imaging (MOI), aiming to explore future development directions for in-line inspection techniques. By modeling, simulating, and experimentally verifying leakage magnetic fields at welds, a systematic comparison was conducted between magneto-optical imaging and the traditional magnetic leakage testing technique in terms of their technical characteristics. The performance of magneto-optical imaging in detecting cracks in girth welds was analyzed. The results demonstrate that magneto-optical imaging can effectively detect closed microcracks in welds, thanks to its high spatial resolution (≤0.1 mm) and area array anti-disturbance feature. However, the engineering application of this technique still faces bottlenecks, including probe reliability, data compression, and recognition algorithms, necessitating targeted technical research in the future to advance the development of in-line inspection techniques.