The full-floor support system of the high-formwork area usually adopts a fastener-type steel pipe frame, but collapse accidents often occur due to uncertain factors in actual projects. In order to study the reliability of the support system, this paper uses the work-risk decomposition tree method to analyse the risk situation of the support system of a specific project. The analysis results show that the risks of formwork erection and installation engineering and concrete pouring in the basic work are relatively large, with risk levels of 32.82 and 32.80 respectively; the two influencing factors of human error and short formwork removal time in the basic risks are the most risky, with risks of 7.3060 and 7.1936 respectively. The safety of tall formwork supports can be effectively guaranteed by ensuring the use of material requirements and avoiding the instability of the support system for local safety control, ensuring the safety of construction workers and maintaining the structural integrity of the formwork system for human safety control, and tracking the entire process of concrete pouring for pouring safety control.