Abstract: Base on the requirement of the calibration for vacuum gauge in operational site,the vacuum calibration apparatus in site has been designed.The calibration apparatus is made up of gas supply module,pump module,pressure decay module,pressure measurement and calibration module and bake module.Consideration the effect of environment in site for vacuum gauge and the requirement of portability and miniaturization for the apparatus,the modularization and split architecture is used in the design.There are three methods for calibrating vacuum gauge.They are static comparison method,dynamic comparison method and pressure decay method.Different modules and methods can be selected to calibrate the vacuum gauge for the different calibration requirement.The calibration range of the apparatus in operational site is 10^-4～10⁵Pa.The combined standard uncertainty is less than 7%.