Rhomboid micro stroke amplifier was designed in order to raise the tilting range of fast steering mirror driven by piezoelectric. Firstly, the theory of stroke amplifier was expounded and the key factors were analyzed with the help of energy method. Secondly, the connection between the performance requirement of fast steering mirror system and key factors of rhomboid mechanism was built. Then, key factors were resolved for self-designed fast steering mirror system. Finally, mode finite element analysis was made for both rhomboid mechanism and fast steering mirror and the experiment was carried out for testing the tilting range of fast steering mirror. The analysis and experiment shows that the tilting range is more than 6′ and the frequency of first mode is about 400 Hz which satisfied the need of fast steering mirror system. The conclusion is that the multiple and the maximum driving force of rhomboid mechanism conflict with each other which can be coordinated by resolving the key factors of rhomboid micro stroke amplifier in order to meet the need of the whole system.