Instruction prefetching technologies proposed for general purpose computer systems cannot meet the requirements of real- time systems. One of the most important issues is that cache content pollution caused by useless prefetching loses real-time tasks' WCET estimates. And a loose on WCET analysis degrades the schedulability of the system and in turn brings down its efficiency. A basic-block based instruction prefetching method is proposed in this paper. The method performs instruction prefetching at the basic block level, avoids useless prefetching, simplifies the instruction hit/miss classifications in the worst-case execution, and reduces the WCET estimates of real-time tasks. Real-time benchmark tests show that, the method can reduce real-time tasks' WCET estimates by 20% and also improve instruction cache access performance by 10% on average.