Taking the cantilevered floor of a gymnasium as the analysis object， the influence of the constraint stiffness of curtain wall on the vibration mode of the floor is studied by numerical simulation and field test. First， the field modal test of the cantilevered floor （including the curtain wall） of the gymnasium is carried out， The stochastic subspace identification approach is used to fit the test data and obtain the vibration mode of the floor under the ambient excitation. Secondly， the experimental mode is compared with the results of finite element simulation， and the finite element model is modified according to the test mode and an equivalent simulation method of curtain wall. The results show that the relative error between the first six frequencies of the measured floor and the first six frequencies of the finite element is less than 5%， the average error of each order is less than 2%， and the mode coincidence is agree well， it is further verified that the support system with high strength such as cantilevered floor contributes to the constraint stiffness of curtain wall and the rationality of an equivalent simulation method.