To obtain the influence of submillimeter-sized gap or cushion on the behavior of flyer driven by the detonation of a triaminotrinitrobenzene（TATB）-based explosive， the precise detonation tests with submillimeter-sized gap or cushion were designed. The velocity histories of flyer driven by the triaminotrinitrobenzene（TATB）-based explosive and influenced by the submillimeter-sized gap or cushion were recorded by a laser interferometer （photon Doppler velocimeter）. The results show that the jump-up velocity of the flyer with the influence of submillimeter-sized cushion is lower than the case of flyer attached to explosive， but the final velocity is higher （around 20 m·s^-1 or 1% of the final velocity）. While the influence of submillimeter-sized gap is greater than that of submillimeter-sized cushion that， the final velocity is 50 m·s^-1 （2%） higher than the case of flyer attached to explosive. Simultaneously conducted numerical simulations show that both the point and line initiation conditions do affect the velocity history of the flyer， and the final velocity increases with the influence of submillimeter-sized gap and with either initiation condition. The theory analysis indicates that the introduction of submillimeter-sized gap between flyer and explosive results in weaker interaction between detonation products and flyer for the isentropic expansion of detonation products， and then leads to less entropy increasement of the system， higher energy for driving the flyer， and higher final velocity of the flyer. Additionally， different gap sizes result in different influences as the dominant mechanism varies.