This paper proposes a design for aerostatic gap adjustment to address the limitation of traditional aerostatic spindles being unable to adjust the aerostatic gap to accommodate various operational states or external loads. A piezoelectric micro-displacement amplification mechanism is employed as the actuator to adjust the aerostatic gap. Theoretical derivations and simulations are conducted to analyze both the designed piezoelectric micro-displacement amplification and overall aerostatic gap adjustment mechanisms. An experimental prototype is developed and tested. The experimental results indicate that the output displacement of the designed piezoelectric micro-displacement amplification mechanism is 518.739 μm at a driving voltage of 120 V, and the corresponding output displacement of the aerostatic gap is 189 μm with a response time of approximately 0.38 s.