The vacuum systems of PLS linac provides average pressure of $2.6 imes 10^{-6}$Pa under high power microwave of 54 MW peak with 4.1 $mu extrm s$ pulse width and 10 Hz repetition rates. The base pressure of system is$2.4 imes 10^{-6}$Pa with 45$^{circ}C$ cooling water. The outgassing rate of the system is decreased from $3.0 imes 10^{-11}Torr-l/sec- extrm{cm}^2$ at the initial stage after installation to $1 imes 10^{-12}Torr-l/sec- extrm{cm}^2$ at present. Total accumulated microwave energy dose is about 140 GJ per module. All ion pumps are working under saturated regime and effective pumping speeds of 60 I/s, 230 I/s ion pumps are 45 I/s, 65 I/s, 140 I/s under the operating range. Main problems occurred in recent year are troubles of ion pump controller and vacuum gauge controller, vacuum leak of energy doubler window and electron gun ceramic, and water leak in the dummy load of acceleraing columns. Total of 41 troubles with 140. 8 hours down time give good system availability of 98%. Down time can be reduced by high power waveguide valves and water dummy loads under development, and then availability is expected to be increased up to 99.5%.