When dark matter annihilation takes place in the Universe at high redshifts (between recombination and reionization), energetic particles are injected into intergalactic medium (IGM), which is filled with neutral hydrogen. By ionizing and heating IGM, dark matter annihilation can affect redshifted 21cm signals, which EDGES have claimed to detect for the first time. After reviewing how redshifted 21cm signals are modified by dark matter annihilation, we revisit the constraints based on the EDGES result. In particular, we’ve performed dedicated N-body simulations in order to estimate dark matter clumpiness, as known as boost factor, which has results in constraints more conservative than previously estimated.