Abstract: Using principle of fluid dynamics and assumption of pressure pulsation accompanying gas bubble and cavitation in hydraulic low pressure pipeline, a pressure transient mathematical model based on the two equations for continuity and motion is presented; the model of friction is developed and the models of gas bubble and growth and collapse of cavitation are set up so as to calculate the volume of gas bubble and cavitation inside the mathematical model. An example of fluid transient inside the hydraulic horizontal pipeline is simulated and tested by finite difference method and Matlab/Simulink. Comparison between simulating results and experimental results shows that the mathematical model and finite difference method can deal with the prediction of pressure transients accompanying gas bubble and cavitation inside hydraulic low pressure pipeline.