The invention provides a test system for synchronously testing a detonation propagation structure in a pipeline with various pipe diameters, and belongs to the technical field of detonation structures. The test system is provided with a gradient-structure round detonation pipeline group, wherein the gradient-structure round detonation pipeline group can be used for displaying changes of a transverse wave structure and a longitudinal wave structure of spiral detonation and comprises a driving segment and test segments with different sizes, hermetic connection of pipelines with different pipe diameters is achieved by a reducing flange, the driving segment is connected with a high-pressure ignition device and is connected with a 80-millimeter pipeline by a flange, the 80-millimeter pipeline is connected with a 60-millimeter pipeline by a reducing flange, a fixed screw is arranged on the reducing flange, and similarly, a 40-millimeter pipeline and a 20-millimeter pipeline are sequentiallyconnected to form the reducing pipeline test system. The transverse wave structure and the longitudinal wave structure of detonation of each segment are recorded by a smoke film attached onto an innerwall of the pipeline of each segment, it is found that the a detonation wave propagating in the pipeline is changed with the size change of the pipeline, contrast analysis with test data corresponding to each single-size pipeline, and the test system is of important significance to research and exploration of a detonation structure.