The defects of a submarine pipeline caused by laying, non-uniform seabed support and impact of falling objects are often distributed in many places. In order to simplify the analysis, the buckling model of a pipeline with multiple elliptical defects in the axial direction is generally simplified as the pipeline with uniform elliptical defects or the pipeline with a single local elliptical defect in the axial direction. However, there are few studies on the differences of these three models and their application in engineering. Based on the numerical simulation, this paper presents a study on the buckling and instability behavior of the pipeline with three kinds of elliptical defects. The RIKS method was used to solve the buckling pressure of the pipeline, and compared with the calculation results of DNV-OS-F101, focusing on the analysis of the excitation position and influence parameters of the buckling and instability of the pipeline with multiple elliptical defects in the axial direction. The results show that the buckling pressure of the pipeline model with different elliptical defects is obviously different, and the order is the buckling pressure of the pipeline with uniform elliptical defects < the theoretical solution of DNV-OS-F101 < the buckling pressure of the pipeline with multiple elliptical defects < the buckling pressure of the pipeline with single local elliptical defects. For the buckling analysis of the pipeline with multiple elliptical defects in the axial direction, if the pipeline model is simplified with axial uniform elliptical defects, it is more conservative. However, if the pipeline model is simplified with axial single local elliptical defects, it is more dangerous. Besides, the buckling pressure of the pipeline with multiple elliptical defects is affected by the size of elliptical defects, the distance between elliptical defects and the length of elliptical defects.