An extended state observer (ESO) based controller with acceleration compensation strategy was proposed to satisfy the high requirements for control performance of fast step/stare imaging mechanisms. First, the theory of ESO was described and its characteristics were expatiated. Then, the third-order linear extended state observer (LESO) was designed with an imaging mechanism as the controlled object. By placing the observer in the feedback channel of the speed loop, a double loop controller of position and speed based on an ESO was designed. On this basis, an acceleration compensation strategy was proposed, and the compensating link was described using the estimated acceleration output by the observer. The experiment results showed that the settling time of the imaging mechanism was reduced at every step from 76 ms to 33 ms and the accuracy of the angular position during the period of stare decreased approximately 0.07°to 0.01°. In addition, the speed fluctuation was reduced by approximately two to three times compared with that without acceleration compensation. The control performance of the mechanism was significantly improved to meet high-performance requirements. The design process of the controller was simple and the adjusted parameters were less than that of traditional designs, which is of high practical value in terms of improving the performance of similar control systems.