Abstract: Truss is a structure composed of members connected by hinges at both ends. It mainly bears axial tension or compression, so it can make full use of the strength of materials. When the span is large, it can save materials compared with solid web beams, reduce self weight and increase stiffness. However, structural collapse oftens occurs due to non-standard construction and poor construction quality. The collapsed truss of a stockyard was taken as the research object. In order to find out the causes of the collapse of the truss, by detecting the material strength, weld size and weld strength of truss members, the actual load of the structure was investigated, the mechanical properties test and numerical simulation analysis of welds were also conducted, it was finally concluded that the root cause of the collapse of the truss was that the weld of the main truss did not meet the requirements of specification and design.