Fluid-structure interaction (FSI) is essentially a dynamic phenomenon and always exists in fluid-filled pipe system. The four-equation model, which has been proved to be effective to describe and predict the phenomenon of FSI due to friction coupling and Poisson coupling being taken into account, is utilized to describe the FSI of fluid-filled pipe system. Terse compatibility equations are educed by the method of characteristics (MOC) to describe the fluid-filled pipe system. To shorten computing time needed to get the solutions under the condition of keeping accuracy requirement, two steps are adopted, firstly the time step △t and divided number of the straight pipe are optimized, secondly the mesh spacing △z close to boundary is subdivided in several submeshes automatically according to the speed gradient of fluid. The mathematical model and arithmetic are validated by comparisons between simulation solutions of two straight pipe systems and experiment known from literature.