Terahertz technology has its unique advantages in the field of biomedicine and is increasingly used in modern medical applications. In this study, to research the responding of biological tissues (cells or nerve nuclei) to various terahertz energy stimulation, an automatic terahertz energy control optical system is designed. The ray tracing simulation of the selfdesigned optical lens model is conducted and the results show that the system can achieve the focusing arrangement within 90 mm and control the strength of terahertz energy on image plane. In addition, an automatic control system with nanometer‐level precision is designed using a stepper motor subdivision scheme to coordinate with the image plane (target point) energy and morphology adjustment. Then biomedical experiments based on this system are carried out. Through adjusting the system, terahertz intensity on cells is changed, so that the cells show various cell viabilities. The optimized experimental results show that the terahertz energy automatic control optical system designed in this study is qualified for terahertz energy irradiation research with biological cells. [ABSTRACT FROM AUTHOR]