Abstract: Soil cracks are often considered to be caused by tensile-shear stress. In actual engineering, the compacted clay is mostly under compressive-shear stress state. In order to explore the crack initiation mechanism of the existing cracks in the compacted clay under compressive-shear stress state, the stress field and fracture criterion of the closed crack are analyzed theoretically. The uniaxial compression tests on the compacted clay with central cracks are carried out. The influence of dip angle, length and shape of cracks on the tensile fracture behavior of the compacted clay are investigated. The applicability of the compression-shear closed-crack tension fracture criterion considering T-stress in the compacted clay is verified, and the compression-shear tension fracture mechanism of closed cracks in the compacted clay is revealed. According to the comparative analysis of the test results and the theoretical prediction curve, the critical size r_c of the compacted clay is about 2 mm, which is obviously smaller than the estimated value of 12 mm by the empirical formula used in the rock field. Through detailed discussion, it is shown that the formula applied in the rock field is not suitable for the compacted clay. In addition, the T-stress is introduced tentatively to establish a compression-shear-tension fracture criterion for open cracks. The differential initiation behavior of closed and open cracks is explained, and its limitations are shown.