To increase system uptime with limited energy, this paper discussed the influencing factors of threshold selection in timeout policies from the point of view of timeout policies in dynamic power management. After investigating domestic and overseas principles of dynamic power management strategies, analyzing principles of dynamic and fixed threshold policies in timeout policies and completing analyses of influencing factors of threshold selection in the present dynamic threshold policies, the paper drew a conclusion of the following three influencing factors on threshold selections, which were energy consumption during hibernating and awakening of system, batteries′ discharge voltage and system′s application environment, respectively. At last, this paper confirmed that comprehensive consideration on threshold influencing factors would be a shortcut in finding optimal threshold.