A multi-information measurement system is used to activate the GaAs photocathode. During the experiment, the curves that show the change of vacuum pressure and photocurrrent are recorded also. The cathode used in the experiment is heavily p-type GaAs (100). The doping concentration is 1×1019cm-3. The cathode is grown by molecular beam epitaxy (MBE) and the thickness is 1.6μm. GaAs cathode is degreased before being sent into ultra-high vacuum system to be heat cleaned. The activation technique is "high-low temperature" two-step activation. High temperature of heating is 600° and low temperature of heating is 410°. During the high temperature activation the integrated sensitivity is 1380μA/lm, the surface escape probability is 0.3 and the electron diffusion length is 3.1μm. During the low temperature activation the integrated sensitivity is 2140μA/lm, the surface escape probability is 0.6 and the electron diffusion length is 3.8μm.