针对基于最小方差的性能评价准则由于只考虑时滞引起的性能限制，不适合对PID控制回路进行性能评价的问题，本文采用PID能实现最小方差控制准则，对四水箱控制系统进行性能分析，得到的性能指标比传统最小方差准则明显提高，控制器参数大大改善了过程的输出方差。实验表明，PID能实现最小方差准则能够为PID控制器的性能评价提供一个合理的评价基准，更说明其对特定类型控制器性能评价所具有的实际意义。

As Minimum Variance Benchmark  considers only the time delay, which leads to the problem of the performance limitation and does not fit to PID controller’s performance assessment, PID Achievable Minimum Variance Benchmark is adopted in this paper to solve the problem of the abovementioned. The performance index  increases obviously compared with the traditional index gained through Minimum Variance Benchmark in the fourtank control system. And the process output variance is reduced by the returning parameters，too. The experimental results not only show that PID achievable minimum variance can provide a reasonable performance benchmark for the PID controller but also indicate that there is more practical significance to study the performance assessment for specific type controllers.