In this paper, COMSOL Multiphysics simulation is applied to acoustic resonant tube experiment. First the sound pressure distribution in the vicinity of tube end is calculated and the departure from the picture given by one-dimensional wave appxoimation is visulized. Then, the shift of resonant frequency is investigated due to the existence of sound detector (microphone). The result shows that the shift, which may be positive as well as negative,depends on the size and position of sound detactor. Finally, the resonant frequency of a tube with partly closed end is calculated and find that the numerical results agree with the mearsured values quite well. The stduy shows that numerical simulations can be applied to undergraduate physics laboratory to help students achieving a better understanding of experiments and endow them with a powerful tool to tackle practical problems.