For the structural columns to be set up in fill walls is an important measure to improve the out-of-plane bearing capacity of masonry structures. In order to address such shortcomings as complex construction, quality assurance, and difficulty in recycling in traditional reinforced concrete structural columns, it is proposed to install square steel tube concrete structural columns in fill walls for a further improvement of the constraint capacity of the wall and the safety of the masonry structure. Based on the out-of-plane loading tests conducted on 6 fill walls, an analysis is made of the bearing capacity of two scaled models of fill walls under different structural columns, followed by a simulation of the out-of-plane ultimate load of the fill walls by using ABAQUS. The experimental results show that the fill walls under the two structural columns are characterzied with the same out-of-plane stress performance, while the confinement effect of the square steel tube concrete structural column on the wall has been improved by 80.3%, and the out-of-plane ultimate load has been increased by 249.9%.