In a method for making a wave-absorbing sheet, first emulsified mixture is provided by mixing wave-absorbing particles with graphene solution so that the graphene solution absorbs the wave-absorbing particles. Secondly, second emulsified mixture is provided by adding and blending resin solution in the first emulsified mixture. Thirdly, third emulsified mixture is provided by adding and blending interface modifier in the second emulsified mixture. Then, two conductive substrates are submerged in the third emulsified mixture, and voltage is provided to the third emulsified mixture so that the wave-absorbing particles, the resin solution and the graphene solution are evenly coated on the conductive substrates. Then, a wave-absorbing sheet is provided by eroding and removing the conductive substrates. Finally, the wave-absorbing sheet is washed and dried. The wave-absorbing sheet is thin, light and flexible, and exhibits a wide absorption frequency band and a high absorption rate.