Active disturbance rejection control technology and its application to trajectory tracking control of a linear actuator are presented in this paper. Working principle of each part of this control technology is given, and parameter tuning method is discussed which helps control engineers to use this technology well. In order to test the performance of active disturbance rejection control technology, a sinusoidal trajectory tracking control system of a linear actuator is constructed. Simulation and experimental results show that the introduced control technology can achieve small tracking error at low velocity where friction is the main disturbance. Active disturbance rejection control technology provides a good choice for control engineers in actual industry applications with its simple structure, convenience to use and excellent performance.