Abstract: To study the effect of the attached mass of the simulated free boundary on the dynamic characteristics of a high-resolution satellite during the ground micro-vibration test, the theoretical model of the free boundary is established with consideration of the attached mass in the satellite underground micro-vibration test. The effect of the attached mass on the modal frequencies and the frequency response is analyzed by combining this theoretical model with the structural dynamics model of a satellite. Furthermore, the dynamic test is carried out for a structural satellite model with different values of the attached mass, and the test result is analyzed. It is shown that the ratio of the attached mass has a significant influence on the modal frequency and, especially, on the frequency response peak. Thus, the attached mass should be controlled within 5% of the total mass of the satellite, to avoid the serious negative influence on the dynamic characteristics of the satellite in the micro-vibration test.