The sudden breaking of the boom cable destroyed the bridge, and the research is very enthusiastic, resulting in such technologies as "short boom" theory, "double boom" theory, "rust breaking" theory and "multi-boom" technology. And so on, there are many opinions, and it is applied in engineering design and accident diagnosis. Small boom, endanger the whole bridge, the problem is: the current design of bridge boom, admit the possibility of failure (probability); Techniques such as "three years of testing "," suspected disassembly ", and" replacement is complete (or batch) replacement "obviously cannot fundamentally rule out the risk of sudden cable breakage. According to the failure analysis (so-called material diagnostics), the common and even coupled action of the arch bridge derrick is multiple factors. Not a single, superficial argument can be summarized. After a brief analysis, discussion and a case study, the author holds that the above theories are flawed, may not be valid, or cannot be established at all. At last, the paper introduces the design of the boom of Xiangshuigou Bridge based on "safety technology of cable breakage", in order to clarify its technical key points and applications, and explore the way to solve the problem.