In order to ensure the safe operation of buried natural gas pipeline (BNGP) under landslide debris flow (LDF), a model is established to investigate the strain characteristic of BNGP. The influence of longitudinal LDF morphology is analyzed for the elliptic deformation rate, tensile and compression strain of BNGP. The results show that the influence area of LDF is about 5 m from the upstream and downstream position of active area, respectively. The peak value of elliptic deformation rate is mainly impacted by the thickness and length of LDF, and will increase linearly with that. The maximum value of axial strains will also increase linearly with length, thickness and breadth of LDF. It will decrease with the angle of mountain slope and depth of BNGP. The fracture failure of BNGP may be occurred at the active area of LDF and upstream position of that. But the local yield or fold failure of BNGP will be occurred at the active area of LDF and downstream position of that. At the same time, a method is proposed to estimate the maximum value of elliptic deformation rate and axial strains of BNGP under longitudinal LDF. The deviations between the prediction results and simulation data are less than +/- 10%.