The invention relates to a test method for simulating long-term deformation of a rockfill. The test method comprises the following steps of: (1) building a strength degradation model according to a rockfill isochronous stress-strain curve acquired by an indoor triaxial test; (2) randomly simulating a three-dimensional rockfill particle set; and (3) calculating and drawing a long-term deformation curve for rockfill particle flowing deformation by utilizing a rockfill particle random model and the strength degradation model. The test method disclosed by the invention has the advantages that the simulation test method can observe slippage, rotating and cracking of a particle in a flowing deformation simulation process in real time, each fabric quantity is conveniently extracted, the long-term deformation curve of the rockfill is drawn according to test data, non-linear stress-strain parameters can be more accurately solved, basis is provided for numerical calculation of a rockfill dam, and certain reference base and theoretical guidance can be provided for researching problems, such as the long-term deformation, of some rockfill dam projects.