To further investigate the compressive mechanical properties of new mold bag concrete for primary support of tunnels, the original test procedure is improved to fulfill the actual construction requirements of mold bag concrete during specimen processing. Accordingly, various test conditions are created for specimens aged 3, 7, and 28 days, and the influence of these mold bags, pressurized drainage pressures, and pressurized drainage times on the compressive mechanical properties of the concrete are analyzed, along with the failure modes of the specimens under various working conditions. The present findings are stated as follows: (1) The mold bags significantly improve the compressive strength and overall deformation capacity of the concrete. (2) The overall deformation capacity and compressive strength of the mold bag concrete vary with the pressurized drainage pressure and pressurized drainage time, and the pressurized drainage pressure over a certain time provides a greater enhancement than the pressurized drainage time under a certain pressure. (3) The normal concrete specimens are damaged in the shape of an angular cone, the nonmold bag concrete specimens are damaged along the parallel direction of the applied load, and the mold bag concrete specimens display a petal shape from the front view.