In the dark age of the universe , any exotic sources , e.g .
the dark matter annihilation , which inject the energy into the intergalactic medium ( IGM ) will left some imprint on the 21cm background signal .
Recently , one new kind of dark matter structure named ultracompact dark matter minihalo ( UCMHs ) was proposed .
Near the inner part UCMHs , the distribution of dark matter particles are steeper than that of the general dark matter halos , \rho _ { UCMHs } ( r ) \sim r ^ { -2.25 } , and the formation time of UCMHs is earlier , z _ { c } \sim 1000 .
Therefore , it is excepted that the dark matter annihilation within UCMHs can effect the 21cm background signal .
In this paper , we investigated the contributions of the dark matter annihilation within UCMHs to the 21cm background signal .