A polarization-insensitive broadband terahertz (THz) metamaterial absorber is presented in this paper. The metamaterial absorber consists of several circular and rhombus metallic patches as a unit cell and a metallic ground plane separated by a polyimide dielectric layer. By increasing the number of circular and rhombus patches with different sizes, the operating bandwidth of the absorber is broadened because of the resonances of each single patch getting close enough and merging together in the frequency range. The simulated results show that the absorption bandwidth covers a broadband frequency range of 0.22-0.33 THz with the highest absorptivity of 99.93% at 0.3035 THz. The full width at half maximum is as wide as 0.155 THz, and the bandwidth of over 80% absorptivity is 0.1315 THz. This study promises applications in THz detection and communication systems, and the operation bandwidth is very convenient and compatible for electronic THz sources.