An axial adjusting mechanism is designed to meet the requirement of long adjusting distance, high precision and compact structure in projection objective, based on triangular switching principle. V-flexure element is designed to achieve the switching and transmission of motion in adjusting mechanism. The parameters of V-flexure element are optimized to satisfy the requirement of adjusting distance, drive force, frequency and ratio of transmission. The influence of changing V-flexure element parameters on mechanism performance is analyzed by finite element analysis method. The result is that the adjusting distance is ±55 μm, the adjusting precision is better than ±10 nm and the frequency is more than 150 Hz. And then thermal deformation of lens is analyzed when the thermal load is 20 mW. The result is that the peak-to-valley (PV) value of the upper surface is 0.087 nm, and the root-mean-square (RMS) value is 0.013 nm. The simulation results show that the influence of axial adjusting mechanism on lens surface figure precision is small. Such an axial adjusting mechanism can satisty the requirement of lithograph projection objective.