<p>As a key pressure-bearing component of deep-sea equipment, the pressure-resistant hull, due to the use of high-strength materials and relatively thick welding processes, is prone to internal defects. During repeated diving operations and surfacing welding in extreme environments, stress concentration and microcrack sources are prone to occur. At present, although eddy current thermal imaging technology has been applied to defect detection, the lack of a unified thermal image processing effect evaluation system has seriously hindered the promotion and application of this technology in engineering practice. This study applied eddy current thermal imaging technology to the detection of microcracks in deep-sea pressure-resistant structures, innovatively established a complete evaluation system for eddy current thermal image processing methods, and solved the application bottleneck of thermal image processing technology in practical engineering. By establishing an objective evaluation index system without a reference system, systematic optimization and comparative analysis were conducted on three typical processing methods: thermal image signal reconstruction (TSR), fast Fourier transform (FFT), and principal component analysis (PCA). The performance of different processing methods in surface defect detection was quantitatively evaluated. The research results show that TSR has a remarkable contrast enhancement ability for cracks with obvious surface features and high signal-to-noise ratio. FFT can effectively extract the unique frequency characteristics of fine cracks. However, PCA demonstrates an irreplaceable ability to separate weak signals in deep cracks with extremely low signal-to-noise ratios. This evaluation system not only provides a theoretical basis for the development of new algorithms, but also offers quantitative guidance for the selection of data processing methods in engineering practice, and has significant theoretical value and engineering application prospects.</p>