Abstract: This study compares the performance of ultra-high performance concrete (UHPC) and conventional concrete in response to contact explosions. Contact explosion experiments were conducted on C150 UHPC and C60 concrete slabs using explosive charges ranging from 1.5 kg to 4.5 kg. The investigation focused on the variations in crater dimensions on both the blast-facing and rear surfaces of the slabs, as well as the corresponding failure modes, in relation to the explosive charge applied. The blast resistance coefficient of the blast-facing surface of the C150 UHPC slab was discussed, and the critical collapse coefficient was provided. The results reveal that the failure mode of the UHPC slabs shifts from crater formation at lower charges (2.0 kg) to severe collapse at higher charges (4.5 kg). C60 concrete slabs experience a transition from moderate collapse to perforation under the same conditions. For the same explosive charge, the diameter of the spall crater on the rear face of C150 UHPC target plates is reduced by more than 21%, and the depth by more than 60%, compared with C60 concrete. The empirical formula for fitting anti-explosion coefficient of conventional concrete is applicable for fitting the blast resistance coefficient of UHPC in the cratering stage under low explosive charge masses, whereas it exhibits poor applicability under high explosive charge masses. The critical collapse coefficient for the C150 UHPC was determined to be 0.208 m·kg^–1/3.