<p>To optimize the construction process, this manuscript introduces the highly ductile concrete (HDC) permanent formwork system, comprising rebar trusses embedded in a 20-mm-thick HDC sheet, as a novel lightweight prefabrication system. The system fully leverages the performance advantages of HDC and factory-prefabricate features. Initially, the flexural properties of the HDC permanent formwork system under construction load were studied experimentally. The results indicated that the designed specimens can meet the code requirements in construction stage. Additionally, the HDC sheet significantly contributes to the overall stiffness of the specimens, with a contribution rate ranging from 35 to 59%. Subsequently, a finite element model of the HDC permanent formwork system based on ABAQUS was developed to compare with experimental findings. The cracking load and initial stiffness derived from ABAQUS exhibited good agreement with the experimental results, with the load–deflection curves of the two largely overlapping. Therefore, the developed finite element model demonstrates sufficient accuracy and can be utilized for real-world applications. Furthermore, parameter analysis revealed that the mechanical properties of HDC permanent formwork system are primarily influenced by top rebar diameter, rebar truss height, span, and HDC thickness, with bottom rebar diameter having minimal impact. Finally, a method was given to calculate the stiffness, deflection, and cracking load of the HDC permanent formwork system. The maximum applicable span of the system in the construction stage was calculated based on this method.</p>