The effect of initial imperfections on the pipeline global buckling is the theoretical basis of the global buckling stability analysis and buckling control of the submarine pipeline. The pipeline length for the analysis has a significant effect on the global buckling. According to the global buckling regularity of pipelines with different length, pipelines are divided into two types: the “long pipeline” and the “short pipeline”. The global buckling of pipelines with different initial imperfections is simulated by the 3D-Explicit method. The effect of an initial imperfection on the global buckling of a “long pipeline” and a “short pipeline” are proposed by analyzing the effect of initial imperfections on the expansion length of buckling. The global buckling of a long pipeline and a short pipeline with the same initial imperfection are compared. It shows that the post-buckling characteristic values, including moment, strain and lateral displacement, of the long pipeline are larger than those of the short pipeline. It shows that the long pipeline with an initial imperfection is more prone to destructive global buckling than the short pipeline with the same initial imperfection.