  Multiband observations on the type Ia supernova remnant SN 1006 indicate
peculiar properties in its morphologies of emission in the radio, optical and
X-ray bands. In the hard X-rays, the remnant is bilateral with two opposite
bright limbs with prominent protrusions. Moreover, a filament has been detected
at the radio, optical and soft X-ray wavelengthes. The reason for these
peculiar features in the morphologies of the remnant is investigated using 3D
HD simulations. With the assumption that the supernova ejecta is evolved in the
ambient medium with a density discontinuity, the radius of the remnant's
boundary is smaller in the tenuous medium, and the shell consists of two
hemispheres with different radiuses. Along particular line of sights,
protrusions appear on the periphery of the remnants since the emission from the
edge of the hemisphere with a larger radius is located outside that from the
shell of the small hemisphere. Furthermore, the northwest filament of SN 1006
arises as a result of the intersection of the line of sight and the shocked
material near the edges of the two hemispheres. It can be concluded that the
features that the protrusions on the northeast and southwest limbs and the
northwest filament in the morphologies of SN 1006 can be reproduced as the
remnants interacting with the medium with a density discontinuity.
