Regarding the practical problems of the real-time task scheduling and analysis in safety-critical systems such as spacecraft, this study proposes a schedulability determination method based on virtual zoom out period, constructing a strong-hard task (SHT) model to accurately describe real-time tasks, and allocates priority based on task’s time characteristics. Virtualizing all strong real-time task as a hard real-time task, virtually reduces the period of the hard real-time task and calculates the worst virtual execution time, and then determines the schedulability according to the RMS schedulability judgment formula. This paper presents a rigorous proof of the method, which can make a fast schedulability determination on an SHT task set containing n tasks, and the time complexity of this algorithm is only O(n²). Comparative verification was carried out on the China space station computer, and the experiments show that the schedulability determination efficiency is better than the existing methods. The average running time overhead is reduced by 41.8%, and the schedulable ratio is increased by 5.7%.