Abstract: Based on static priority scheduling algorithm in hard real-time multitask system,and incorporating other time overhead besides execution time of the tasks,for example,tasks synchronization interruption processsing,this paper quantitativly analyses the influence of time parameters upon tasks deadline,and presents a method used to calculate whether a task can be completed within specified deadline.The method treats timm-out as a kind of fault,then gets the probability of time-out fault occurring,and provides a quantified means for evaluating real-time feature.