Abstract: Using an onerdimension hybrid code, we numerically studied the interachorbetween tWo kinds of interplanetary structures (the plasmoid with high density andinterpanetary shock) and the quasi-parallel collisionless shock. The results show thatdue to the scarering of large-amplitude ultralow-frequency upstream waves, theplasmoid with high density begins to diffuse in the upstream, and it diffusesconhnuously in the downstream besides a little compression when it passes through theshock ramp. When the interpanetary shock close to the quasiparallel collisionlessshock,large-amplitude ultralow-frequency waves are formed in the upstream of theinterplanetary shock, and the sbength of the interplanetary shock are enhanced. Finallythe two shocks merge as a new shock which excites large-amplitude ultralow-frequencywaves in the upstream.