Faced with the problem in quantitative evaluation methodology in China,namely research institutes are usually ranked only by R&D outputs or even the sum of the input and output under some weights, the article has imported economic views and established an evaluation model based on the knowledge production function to reflect the outputs, the inputs and input elasticity in theory. Results of the application in CAS show that the model preferably solved the problems of ignoring inputs, unfairness between subjects etc., made it possible to compare institutes of the same kind both in column and in landscape orientation, and provided quantitative gist for the performance evaluation of public R&D institutes.