Usually, pressure fluctuation in oil pipeline is assumed to be stochastic or as white noise, which hinders the improvement of fault diagnosis technology based on pressure fluctuation. To find the internal dynamics of pressure fluctuation in oil pipeline, the possibility of existing chaotic behavior is validated using the method of nonlinear analysis. Six experimental data sets are studied on which phase spaces are reconstructed, the fractal dimensions and Lyapunov exponents are computed and the stationary feature and nonlinearity are validated. By the analysis of the results, the rigorous chaotic character of pressure fluctuation in oil pipeline is found, which is a theoretical basis for the correlative investigation based on pressure time series of oil pipeline.