The safety cover thickness required for TBM （tunnel boring machine）tunneling in hard rock is such that it is too large to increase the total length of the tunnel design without increasing the cost. Therefore, the study of the minimum safety cover thickness for TBM tunneling in hard rock is of great engineering significance. The Guangzhou-Dongguan-Shenzhen Intercity Railway Xixiang Station - Bao'an Station double-mode shield tunnel project case was drawn upon to investigate the minimum safe overburden thickness of varying parameters under the condition of changing rock grades. The results indicate that when the arch displacement method is employed, if the tunnel perimeter rock class is II or III, and the thickness of soft soil is between 0 and 3 times the diameter of the tunnel, then the minimum safe rock cover thickness is between 0.2 and 1.2 times the diameter of the tunnel. When the pressure arch method is employed for simulation, if the rock cover class is II or III, and the soft soil thickness is between 1 and 3 times the tunnel diameter, the ratio of the minimum rock cover thickness to the depth of burial exhibits a tendency to increase and then decrease with the increase of the hard rock thickness，reaching a maximum value of 0.39. When the overburden grade is grade IV and the thickness of the soft soil is 1 to 3 times the diameter of the tunnel, the ratio of the minimum rock cover thickness to the depth of burial is observed to decrease with the increase of the hard rock thickness, reaching a maximum value of 0.42. The conclusions can provide engineering guidance for TBMs to safely tunnel through hard rock.