Abstract: The TOFD (Time of Flight Diffraction) detection technology has many limitations, such as blind spots on the upper and lower surfaces and their spatial resolution limitations. Relevant domestic and foreign technical standards have long paid attention to these issues and described the calculation methods for TOFD detection of blind spots on the upper and lower surfaces and spatial resolution. However, in practical applications, relevant testing standards rarely closely combine the limitations of testing techniques with specific testing processes. The standard NB/T 47013.10—2015 “Non destructive Testing of Pressure Equipment Part 10: Diffraction Time Difference Ultrasonic Testing” proposes specific requirements and targeted solutions for blind spots on the upper and lower surfaces. However, there is less attention paid to the spatial resolution during TOFD testing and the important impact of spatial resolution on testing, especially when the spatial resolution is insufficient, the testing process will conflict with the acceptance standards. The paper started from three aspects including the main impact of spatial resolution on defect assessment, the reasons for its occurrence, and the degree of its impact. The contradiction between spatial resolution and acceptance standards was proven. The universality and importance of spatial resolution issues were analyzed and some shortcomings of relevant regulations in current standards were pointed out.