The invention discloses a method for testing system-level trial run operation modes and operation deformation of liquid rockets. The method includes steps of determining measuring points; mounting sensors; constructing testing systems; debugging the testing systems; measuring data in trail run procedures; analyzing results and the like. The method has the advantages that kinetic characteristics of rocket body structures of the rockets in ignition states can be truly acquired, main low-frequency vibration characteristics of rocket bodies can be obtained by the aid of the few measuring points, and the multipurpose data are acquired and can be used for analyzing the operation modes, analyzing the operation deformation, formulating mechanical environments and the like.