Terahertz absorbers can be widely used in research fields such as military equipment and sensing instruments. Therefore, a polarization-insensitive terahertz metamaterial absorber with a fourfold symmetrical structure is proposed, and the absorption mechanism and influencing factors of the structure are analyzed by changing the structure size and current distribution in this paper. Experimental results show that the resonance frequency of the absorber is in the terahertz frequency band and the absorption rate can reach 99.98%. In order to make the application range of the terahertz absorber wider, two polarization-insensitive terahertz absorbers with adjustable frequency are further proposed. The simulation results of the electromagnetic simulation software CST show that the terahertz metamaterial absorber has high absorption rate, good frequency adjustment performance, and is insensitive to polarization angle, which has great application research significance.