Abstract: To study the blast resistance of reinforced concrete (RC) slabs and retrofitted RC slabs with different methods, the damage characteristics of RC slabs and retrofitted RC slabs with steel plate, polyurea, and ultra-high performance concrete (UHPC) were systematically analyzed through explosion tests and numerical simulations. Firstly, explosion tests of RC slabs and retrofitted RC slabs were conducted, and free field overpressure-time history, as well as the damage and deformation of slabs were obtained. Then, numerical simulation models of ordinary RC slabs and retrofitted RC slabs were established, and the accuracy and applicability of the models in characterizing damage under blast load were further verified based on the test data. The critical scabbing scaled distance of slab was further analyzed through the verified simulation model. Finally, based on the tests and numerical simulations, the influence of blast distance, retrofitting method, and repeated explosion effects were discussed, and the anti-blast retrofitting design suggestions were proposed. Results show that: The slab exhibits front crater, back scabbing and crack of concrete, as well as the uplift of steel plate and polyurea layers under blast load; With the increase of blast distance, the damage degree of ordinary RC slabs gradually decreases, with a critical scabbing scaled distance range of 0.46 m/kg^1/3-0.58 m/kg^1/3; the deformation of steel plate and polyurea in retrofitted RC slabs also decrease, with a notably lower critical scabbing scaled distance range of 0.3 m/kg^1/3-0.46 m/kg^1/3; All the three retrofitting methods can effectively improve the blast resistance of the structure, with the steel plate retrofitting method demonstrating the best performance in suppressing back scabbing and fragment scattering, as well as resisting repeated explosions; Repeated explosions significantly exacerbate the degree of damage and deformation to the slabs, especially the UHPC retrofitted RC slab; For the anti-blast retrofitting design of RC structures, three retrofitting methods were proposed, i.e., UHPC retrofitting on the front surface, steel plate or polyurea retrofitting on the back surface, and combined retrofitting.