This paper analyzes the time parameters of information, considers numerous characteristics including information value, information efficiency and so on, and proposes an accurate mathematical model for information timeliness. The mathematical model makes use of the active information-utilization-window (IUW) to analyze information value, effect of information efficiency on information timeliness, thus obtains the best IUW. With this window, the relationship among information timeliness, time-sensitive and time efficiency can be analyzed by using simulation. The method increasing information timeliness, proposed in this paper based on our analysis, is able to provide theoretical foundation for utilizing information of satellite network more reasonable.