BEPCⅡ，a linear accelerator, developed by institute of high energy physics of Chinese academy of sciences, is an electron-positron collider beam accelerator. It is modified on the basis of the BEPC linear accelerator, which is mainly consisted of the electron gun, accelerating tube, positron source, beam detector, klystron modulator, waveguides, etc. To meet the needs of the BEPCII, linear accelerator needs to operate in the high vacuum state to reduce the scattering effect of residual gas on beam flow. That is why a full transformation was made to vacuum system, including the pump configuration, vacuum pipe layout, measuring system and the valve controller upgrade, and klystron, positron source, vacuum transformation of waveguide valve. All vacuum components were designed and fabricated in strict accordance with the ultra-high vacuum process, which ultimately reached the standard of design acceptance index in advance. And the vacuum value: electron gun: P≤6.7×10-7 Pa, accelerating tube center: P≤6.7×10-5 Pa, klystron output window: P≤6.7×10-6 Pa.