Abstract: For the further study of mechanics properties and failure characteristics of a U-type confined concrete arch, the load, lateral pressure coefficient, stiffness ratio, high-radius ratio, and other factors were considered to establish the mechanical model for an arbitrary section U-type confined concrete arch, with straight leg semicircular arch as an example, so as to acquire the theoretical calculation method for a straight leg semicircular arch. At the same time, the mechanical properties and failure characteristics of a U-type confined concrete arch were analyzed, the test system of an underground confined concrete arch with the scale ratio of 1:1 was developed, and the correctness of the calculation theory for a U-type confined concrete arch with arbitrary section numbers was verified by comparing with the results of numerical calculation and the entity proportion of laboratory test. The research shows that the internal forces are greatly influenced by loads, lateral pressure coefficients, and high-aspect ratios. The internal forces of the two biggest parts in the theoretical calculation are located in the straight leg of 3/4 height and vault. In a pressure case, the straight leg semicircle arch deformation pattern is "vault, arch legs inside collect, the whole becoming tall". The research results can provide a theoretical and experimental basis for the research of mechanics properties and failure characteristics for a U-type confined concrete arch, and provide a guidance for the practice of engineering design.