Evaluation plays an important role in measuring science & technology exhibitions' function and value. After analyzing and comparing the development course and current situation of evaluation of science & technology exhibitions both in America and China, some differences have been found. Firstly, evaluation of science & technology exhibitions in America emerged in the beginning of the 20th century, and has formed a quantitative-focused evaluation system including front-end, formative, remedial, and summative evaluation so far. While Chinese researchers had not paid attention to the evaluation of science & technology exhibition until the 1980s, thus carrying out visitor studies and evaluation practices far less than American works. Secondly, there are institutional demands of evaluation for government-funded science & technology exhibitions, yet Chinese government has no such requirements. Thirdly, evaluation practices of science & technology exhibition in America and China vary in type, evaluator, content and tools.