Abstract: The unsteady flow in oil pipeline can be effectively analysed by use of different numerical methods as well as computers. The most commonly used numerical methods are method of characteristic, explicit difference and implicit finite difference. The analysis in the paper shows that the methods of characteristic and explicit difference, though being capable of dealing with various boundary conditions, have small time steps and need many times of calculations; and that the implicit finite difference method, having longer time step and fewer times of calculations, needs to solve unwieldy nonlinear equation groups. So a method of mixed analysis is introduced, a method that makes the analysis of unsteady flow using both the method of characteristic and implicit difference. During analysis, these two methods are used alternately based upon the length of pipeline, complexity, boundary conditions, and accuracy requirements so as to get proper time step, avoid the nonlinear equation groups and reduce the computer storage and calculation time. Also, based on this mixed method, a software package is developed for analysis of unsteady flow in oil pipeline or pipe network, which is proved feasible by numerious examples.