This paper describes the method used to characterize the zero-pressure effective area (A0) and pressure distortion coefficient () of 200MPa-CCPG oil piston-cylinder unit (PCU) in order to realize the national pressure scale from 1.5 kPa to 500 MPa. The A0 was determined by cross-floating method from a set of primary gas pressure standard, while the H-W method was used for calculating . A set of three oil PCUs was maintained as a primary pressure standard and used for scaling up and down pressure to determine  for the other PCUs. The relative standard uncertainty of 200MPa-CCPG pressure standard is 3.010 -5 .