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Primordial black holes (PBHs) formed in the early Universe can accret darkmatter particles due to gravity and form ultracompact minihalos (UCMHs). Thetheoretical researches and simulations have shown that the density profile ofdark matter in UCMHs is in the form of $\rho (r) \sim r^{-2.25}$. Compared withthe popular dark matter halo model, e.g. NFW model, dark matter annihilationrate is larger in UCMHs. Considering dark matter annihilation, there is amaximum core density $\rho_{\rm max}$ in UCMHs which has been treatedindependent on redshift. While in this work, we point out that $\rho_{\rm max}$depends on redshift and dark matter annihilation rate in UCMHs also changeswith time. We re-investigate the $\gamma$-ray flux from UCMHs due to darkmatter annihilation and focus on their contributions to the extragalacticgamma-ray background (EGB). Utilizing the EGB data of Fermi, the constraints onthe abundance of PBHs are derived, $\Omega_{\rm PBH,EGB} \lesssim 2\times10^{-8}$. Motivated by the recent observations of global 21cm signals by theEDGES experiment, we investigate the influences of dark matter annihilation inUCMHs on global 21cm signals and derive the constraints on the abundance ofPBHs, $\Omega_{\rm PBH,21cm} \lesssim 2\times 10^{-10}$. The derivedconstraints are valid for mass range of $10^{-6} M_{\odot} \lesssim M_{\rm PBH}\lesssim 10^{3} M_{\odot}$.

The abundance of primordial black holes from the global 21cm signal and extragalactic gamma-ray background