Abstract: For ionization gauges,the Electron Stimulated Desorption(ESD) effect and soft X-ray effect are the two significant factors to impact the lower limit of the vacuum measurement.A new ionization gauge has been developed,which was based on the energy filter analyzer.Performances of the gauge have been studied on the extreme high vacuum calibration apparatus,such as the ion current under different system pressure or with different emission current from the cathode,ESD effect and soft X-ray effect.According to the experimental results,under the pressure order of magnitude of 10^-8 to 10^-6 Pa,the ion collector can get the maximum gas phase ion current as the voltage of the energy filter is lower than that of grid for about 25 V.With the system pressure within 10^-8~10^-9 Pa,more gas phase ions could be collected with the emission current of 2.5 mA than that of with 1 mA.The voltage difference for the energy filter analyzer to separate gas phase ions and ESD ions is about 30 V on average.Furthermore,the intensity of ESD phase ions from the anode could be eliminated by the electron bombardment degassing process to about 37.5% before the degassing process thereof.The background intensity caused by soft X-rays was equivalent to a pressure of about 9×10^-11 Pa.