Abstract: To solve problems of system performance degradation caused by nonlinearity such as friction and parameter drift，an integral sliding mode controller for armored vehicles steady sighting system based on extended state observer(ESO) was designed. An error integral compensation term was introduced into the sliding surface based on the state variables in order to reduce the steady state error and break the restrictions that the derivative of the tracking signal must be known. The ESO was introduced to estimate and compensate the inner and outer disturbances of the system, which could help to reduce the required value of switching gain for sliding mode control method and weaken the chattering phenomenon of the system．The simulation and experiment result shows that the tracking accuracy keeps within 0.5% and the max system steady error is less than 0.1 mrad, which implies that the method can restrain the influences caused by the diversified nonlinearity and improve the system performance effectively.