Voids are viewed as one of the most significant manufacture defects found within the composite T-joints and have been demonstrated to reduce their mechanical performance. In this work, the random vibration was introduced into the curing process with vacuum bag pressure to minimize the void content and improve the mechanical behavior of the composite T-joints. The range of accelerations was covered from 5 to 15 g, for different period of random vibrations. Identical static samples were produced by autoclave process with different pressures. The effects of application of random vibration on void content and mechanical performance were comprehensively assessed by combining the microscopy method and pull-off test. The results reveal that application of random vibration can improve the fluidity of matrix, impede the void growth, while, at the same time, develop the adhesion between fibers and matrix. For this reason, void content was reduced to less than 1%, and their morphological characteristics were similar to the pattern cured under high pressure. With the large observed decrease in void content, the ultimate pull-off load increases from 1006 N to higher than 3000 N compared to 0 MPa autoclave process. Meanwhile, significant successive cusps were formed along the crack propagation direction on the fracture surfaces due to the improvement of the fiber-matrix bonding caused by application of vibration, which indicated that the carrying capacity in direction perpendicular to fibers was improved. Therefore, application of random vibration could reduce the dependence of final forming qualities on high curing pressure.