Abstract: Since the different cesium and oxygen currents during the activating process may cause the undefined influence on the sensitivity and stability of GaAs photocathodes, the long-term research was implemented. For the purpose of increasing sensitivity and stability of GaAs photocathodes, three different cesium-to-oxygen current ratios (fixed cesium current and alterable oxygen current) were used to activate the similar GaAs photocathodes, and three sets of experimental results were obtained. The analysis results of experimental data show that the appearance times of photocurrent are almost identical and the peak values of the first photocurrent are very close; ICs/IO=1.07 is the optimum current ratio for high sensitivity and high stability, ICs/IO=1.10 is for low sensitivity but high stability, and ICs/IO=1.03 is for high sensitivity but low stability. Based on the double-dipole model, the stable and uniform double-dipole layers of GaAs-O-Cs:Cs-O-Cs are formed and negative electron affinity is achieved on GaAs surface activated by cesium and oxygen, which cnsists with the analysis results for theexperimental data. The effective technical method can be used to improve the sensitivity and stability of GaAs photocathodes.