Abstract: To study the vertical vibration characteristics of friction single pile and pile group in multi-layer soil, a series of field vertical pile foundation dynamic tests were carried out, and a vertical calculation model of friction single pile and pile group in multi-layer soil was established, and a theoretical calculation method of dynamic response of single pile and pile group was obtained. The displacement amplitude, acceleration and dynamic stiffness of single pile and pile group under vertical dynamic load are obtained through field test, and the interaction law of pile group in the process of vibration is analyzed; Comparing the dynamic stiffness of pile head obtained from the test with the theoretical calculation method, the correctness of the obtained results is verified. The dynamic stiffness of pile group head, the interaction coefficient of pile group and the dynamic efficiency coefficient of pile group are obtained by the calculation model. The analysis of numerical examples shows that there is interaction between piles in the process of vibration of pile group, which leads to the non-multiple relationship between the dynamic stiffness of pile group head and the dynamic stiffness of pile head of single pile; The interaction between piles decreases with the increase of pile spacing and the decrease of pile number.