To test the control performance of attitude control software in real time for a micro-nano satellite under hardware limited, a real-time testing system for the attitude control software of micro-nano satellite was established and the control software was tested with the proposed system. Based on the dynamics and kinematics of satellite attitude, the environment information of satellite trajectory, and the mathematical model of an attitude control algorithm, a flight imitation platform for the micro-nano satellite was developed on a PC. Then, the efficient communication link between on-board computer and PC was established by a Controller Area Network(CAN) and serial communication. The main program of the attitude control software was also modified as required. Finally, the real-time control performance of the attitude control software for on-board computer was tested with the real-time testing system. Experimental results indicate that the attitude control software can complete the initial control stage and enter the bias three-axis stabilization mode by 18 446 s after the separation of satellite and rocket, which achieves the stabilization control of micro-nano satellite attitude. In the bias three-axis stabilization mode, the minimum one-axis attitude accuracy and the angular velocity stability of the satellite are within ±1.86°and ±0.048(°)/s, respectively, which meets the requirements of attitude accuracy and converge time of the control mode.