A strong mainshock seismic usually triggers numerous aftershocks within a short period. The mainshock will cause damage to dam body， and aftershocks have a potential to cause additional damage to mainshock-damaged concrete gravity dam. However， most studies on effect of mainshock and aftershock seismic to dam only consider the mainshock and one aftershock so in order to comprehensively evaluate the damage of numerous aftershocks seismic， a method based on concrete damage plasticity model combined with the P-D-ε curve of hydraulic concrete and hydraulic fracturing effect is taken into account in this study. Therefore， the accumulated damage of concrete gravity dam under single mainshock and main-aftershock seismic sequences are presented. The result show that the structure of dam may be slightly cracked with moderate damage under single mainshock， but aftershock seismic and hydraulic fracturing effect have a significant impact on the accumulated damage of dam body. The main damage area of dam body is concentrated the near of dam heel， the surface of foundation and the upstream break point， with the increase of the number of aftershocks the penetrating crack formation.