Abstract: We developed an instrument for gas pressure calibration based on optical resonance cavities, the so-called optical pressure gauge. Two independent optical pressure gauges were calibrated by a piston pressure gauge with a stated uncertainty of 0.001 1%（k=1）. The uncertainty budget of the optical pressure gauge was systematically analyzed, and the overall uncertainty of the system was obtained. The optical pressure gauge was used to calibrate a commercial capacitance diaphragm gauge with a stated uncertainty of 0.025% several times during a period over one year. The results show that the uncertainty can reach 0.003% within one year after calibration. The results demonstrate the use of the optical gauge in calibrating commercial gauges with high accuracy, and also indicate a good long-term stability of the optical pressure gauge. The instrument therefore can be applied to calibrate various commercial pressure gauges to improve the uncertainty of actual measurement.