In order to test the ablating accuracy and stability of excimer laser corneal ametropia cure system in refractive surgery, a method based on depth measurement of PMMA plate is proposed. Firstly, the theoretical value of corneal ablation depth is analyzed. Then the reasons of the difference between the measured ablation depth and estimated ablation depth of different excimer laser machines are analyzed. Finally, the relationship between the estimated ablation depth of cornea and the measured depth of PMMA plate is fitted and the fitting line is taken as the theoretical value. The experimental results show that by measuring the depth of PMMA plate pre-operation in operation mode and comparing it with the theoretical value, the error of the indicated value is within ±5%.