Abstract: The frequency spectra at lateral bending free vibration of the pile, which is long enough both above and beneath the ground surface, is discussed by means of theoretical analysis and finite element method. The relationship between the modulus of subgrade and frequency spetra is explained. The influence of the water inside and outside of the pipe pile on the frequency is investigated and a coefficient is obtained from experiment. Finally, the frequency of a large scale steel pipe pile is calculated. The results are compared with the in-situ mpasurements, it shows that they are in good agreement.