On base of the principle of bulge/blister, special experimental equipment adapted for precise quantitative evaluation of the adhesive strength of diamond thin films was designed and fabricated, and free-standing windows sample of diamond thin film was fabricated by a new method developed on the base of conventional process technology of Si plane, which can ensure full diamond coatings from damage during the process of etching the free-standing windows. The average adhesion strength of diamond thin films calculated from the tests of the square membranes is 4.287 26 J/m2, which was coincident with simulation outcomes, so it was approved that the initial calculating model was validity. According to these test results, the adhesive strength could be obtained precisely and quantitatively by bulge/blister test, which can provide a basis for the optimization of diamond thin films fabrication technics and a criterion for the quality evaluation of diamond thin films, and the results will be beneficial to wide application of diamond thin films in the tool-engineering field.