British Science Festival (BSF) is the oldest science festival in the United Kingdom, with great impact not only in Europe but the whole world. It has established a stable evaluation system for decades gradually. Some results have been found after the evaluation aims (targets), evaluation contents and evaluation methods of BSF are analyzed, revealing the differences between the perspectives, investigating questions of internal evaluation and that of external evaluation. Firstly, in terms of evaluation guideline and method (internal or external), there is a certain gap between BSF and international leading evaluation system such as NSF which pay more attention to visitor evaluation. However, internal evaluation has advantages in accumulating experience, and improving the overall strength of the working group. Secondly, evaluation plays a significant role in examining aims, output, organization and operation and communication effects on audience but is still superficial and not objective enough. The BSF evaluation system could be a reference in inspiring Chinese peers to establish its own science festival evaluation system and further improvement.