Finite element software ANSYS was used to calculate the natural frequency of tube in a shell and tube heat exchanger.The calculation result was compared with the analytical results by using the related standards (GB 151-1999 and TEMA) and empirical formula (Macdaff-Felga).The natural frequency of tube calculated by the finite element method is consistent with those calculated by GB 151-1999 and Macdaff-Felga,and the frequency calculated by TEMA is smaller compared with those calculated by other methods.The finite element computation also shows that the first mode of baffle lies between the first mode and the second mode of tube.