A broadband graphene absorber with simple structure is proposed in this paper. The substrate used in this paper is 1.3 mm in thickness and constructed with 0.6 mm depth grooves periodically, which can be treated as substrates with a thickness of 1.3 mm and 0.7 mm arranging periodically. The combination of quartz substrate with different heights can realize the superposition of two adjacent frequency bands which leads to broad band characteristic of the absorber. The absorption rate of the absorber is obtained by software High Frequency Structure Simulator (HFSS) 14.0. The relative bandwidth for the absorption rate above 90% is 27.1%, from 134 GHz to 176 GHz. The graphene absorber proposed has potential in the development of stealth technology.