The invention provides an instruction prefectching content selecting method for optimizing WCET (worst-case execution time) of a real-time task. A hardware structure of a basic-block information table (BBIT) is added in high-speed caching hardware of an existing instruction. The instruction prefectching content selecting method includes: initializing hardware configuration, collecting a static routine base block set via a compiler or a static routine character analyzing tool, removing base blocks only covering one storage block, collecting execution frequentness of every program base block under worst-case execution condition, sequencing the program base blocks according to the execution frequentness, selecting information of an appointed amount of program base blocks according to the sequence, and storing the information in the BBIT. During a high-speed cache accessing process, high-speed instruction cache and the BBIT are searched at the same time, high-speed instruction cache accessing loss under the worst-case execution condition can be effectively avoided, requirements on the real-time task are met, and meanwhile, the instruction prefectching content selecting method can effectively reduce hardware design cost, and is simple and direct to realize.