The invention provides a fixed-altitude fixed-speed under-measurement interference suppression attitude control method only using a star sensor. The method comprises the steps that 1) a synchronization signal sent by a control computer is received by the star sensor, so that the measurement moment of star sensor measurement data is synchronized with a control period of the control computer; 2) according to whether new star sensor measurement data are sent back in a current control period or not, the interference torque estimation value Md, i at the current moment is obtained; and 3) the control torque is obtained by calculating the output of a controller, and attitude control over a spacecraft is completed. By adopting a feedforward compensation method, the negative influence on the attitude and angular velocity of the spacecraft is quickly eliminated, the stability of the altitude is ensured, guarantee conditions are provided for normal work of the star sensor, and the continuity of the star sensor data is ensured.