In heterogeneous fault-tolerant system, especially high performance computer system, the issue of providing system with high availability assurance for real-time applications which have availability requirements has been widespread concerned. While, few research concentrates on combining real-time application availability requirement with scheduling algorithm. In this paper, an availability approached task scheduling algorithm is proposed. On the basis of heterogeneous fault-tolerant system scheduler and scheduling algorithm designation, we can improve the system availability without increasing additional hardware costs, and shorten task average response time, in addition, schedule task with high efficiency and reliability. Experiment results show that, such availability approached task scheduling algorithm has a system performance advantage over the traditional system task scheduling algorithms, it achieves the goal of balancing availability and task response time in heterogeneous faulttolerant system, thus improve the system availability.