The initiation behavior of covered explosives by reactive fragments was studied by ballistic experiments, and its initiating ability was compared with that to the explosive subjected to impact of the tungsten alloy fragment having the same mass as the reactive ones. The shock initiation behaviour of fragments to covered explosives has been simulated in the platform of AUTODYN-2D, and the initiation mechanism of reactive fragment was distinctly obtained by comparison of the numerical and experimental results. The research shows that the reactive fragment with a mass of 10g and a velocity above 1287m/s is able to initiate the Composition-B covered by a 10mm thick aluminum plate or a 6mm thick A3 steel plate. However, the tungsten alloy fragment only results in mechanical damage on the covered explosive and fails to initiate the Composition-B at an impact velocity of 1527m/s. The dominant initiation mechanism of reactive fragment to covered explosive is the violent chemical reaction of reactive materials inside the explosive, which decreases significantly the demand of kinetic energy for the fragment.