An orifice flow system has been developed indigenously which is a primary standard for the calibration of high vacuum gauges in the range of 10-3–10-6 mbar. It consists of a constant-volume flow meter, designed to generate a known flow rate of a particular gas to the vacuum chamber. This chamber is partitioned into two parts by a plate with an orifice of calculable conductance. The pressures, generated by this standard system, are compared with those of secondary standard, namely, spinning rotor gauge. Different uncertainties and correction factors are calculated. The maximum percentage deviation is from 1.16% to 0.97%. The combined uncertainties over the entire calibration range of the standard system are in the range of 4.0×10-6 mbar.