In the context of rapid development of terahertz communication technology, the complex scattering property of wireless channel caused by building occlusion, bad weather and other reasons poses new challenges on secure and reliable data transmission. The confidentiality property of terahertz communication contains risks such as leakage and eavesdropping under the wide area of the communication network. Investigations on the feasibility of existing encryption and anti-eavesdropping methods in terahertz communication systems, promoting the innovation and application of physical layer security technology, and achieving stable and secure data transmission have become a valuably urgent topic. In this paper, from the perspective of secure communication, some of the existing physical layer encryption and anti-eavesdropping methods are presented and analyzed; their fusion applications and efficiencies in terahertz communication are summarized; and the trends on future development are expected.