Recently, metasurfaces have received widespread attention due to their unique properties and potential applications in many fields such as biosensing, imaging, and communication. Among these studies, metasurface absorbers have aroused much interest of researchers. Absorbers can perfectly absorb incident certain frequencies or some frequencies of electromagnetic waves, and are widely used in fields such as electromagnetic compatibility and electromagnetic shielding. Compared with traditional absorber materials, a metasurface absorber overcomes the disadvantages of large volume, heavy weight, and poor stability. To cope with diverse application scenarios, it is essential to achieve frequency tunability of a metasurface absorber.In this paper, we propose a liquid crystal-based tunable terahertz metasurface absorber with the advantages of simple structure, and wide-angle stability. By utilizing the electrically tunable property of liquid crystal materials, the absorption frequency of the metasurface absorber can be tuned. Using the dielectric constant tensor of liquid crystal materials for material modeling, the anisotropic properties of liquid crystal materials were simulated. To improve the design efficiency and achieve good absorption and tunability performance, the Particle Swarm Algorithm (PSO) was used for reverse design of the parameters of the meta-surface unit structure. We investigated the absorption characteristics, frequency tunability, and polarization characteristics of the meta-surface absorber obtained by reverse design under vertical incidence, as well as the electromagnetic wave absorption characteristics at different incident angles. The results show that the absorbers with good absorption and tunability performance can be reverse designed efficiently by PSO. By applying voltage to the metasurface absorber obtained by reverse design, and continuously tuning the voltage in the range of 0~10 V, the TE mode absorption frequency is continuously tunable in the range of 404.4~444.4 GHz, with a frequency tunability of 9%. The TM mode absorption frequency is continuously tunable in the range of 404.4~425.4 GHz, with a frequency tunability of 4.64%. Both modes have absorption rates greater than 99%. In addition, the absorber has a large-angle incidence stability. Even at an oblique incidence angle of 60°, the absorption rate is still greater than 94%, and the absorption frequency is stable. The proposed terahertz metasurface absorber has many advantages, such as high absorption rate, wide frequency tunability, and wide-angle stability, which has broad application value.