A folding steel arch frame applicable to mechanized assembly is designed based on a new multifunctional working trolley and the construction technology of prefabricated tunnel and underground engineering to improve the quality and efficiency of tunnel arch erection, and to solve the problems of artificial arch erection in tunnel construction, such as weak connecting point, dislocation, and high labor intensity. Furthermore, a field test on the folding steel arch′s assembly performance and the numerical analysis of its bearing characteristics are conducted using the mechanized assembly construction of the entrance section of New Wushaoling tunnel as an example. The results show the following. (1) The assembly performance of the folding steel arch frame can satisfy the requirements of tunnel mechanized assembly. (2) The folding steel arch frame′s bearing capacity can satisfy the design requirements, and the tunnel′s crown settlement in the test section is 70.6 mm. (3) The use of folding steel arch frame can improve the installation quality and efficiency while reducing labor intensity. Finally, the folding steel arch frame′s key techiques are summarized.