CIT 6 is a carbon star in the transitional phase from the asymptotic giant branch ( AGB ) to the protoplanetary nebulae ( pPN ) . Observational evidences of two point sources in the optical , circumstellar arc segments in an HC _ { 3 } N line emission , and a bipolar nebula in near-infrared provide strong support for the presence of a binary companion . Hence , CIT 6 is very attractive for studying the role of companions in the AGB-pPN transition . We have carried out high resolution ^ { 12 } CO J =2–1 and ^ { 13 } CO J =2–1 observations of CIT 6 with the Submillimeter Array combined with the Submillimeter Telescope ( single-dish ) data . The ^ { 12 } CO channel maps reveal a spiral-shell pattern connecting the HC _ { 3 } N segments in a continuous form , and an asymmetric outflow corresponding to the near-infrared bipolar nebula . Rotation of the ^ { 12 } CO channel peak position may be related to the inner spiral winding and/or the bipolar outflow . An eccentric orbit binary is suggested for the presences of an anisotropic mass loss to the west and a double spiral pattern . The lack of interarm emission to the west may indicate a feature corresponding to the periastron passage of a highly eccentric orbit of the binary . Spatially-averaged radial and spectral profiles of ^ { 12 } CO J =2–1 and ^ { 13 } CO J =2–1 are compared with simple spherical radiative transfer models , suggesting a change of ^ { 12 } CO/ ^ { 13 } CO abundance ratio from \sim 30 to \sim 50 inward in the CSE of CIT 6 . The millimeter continuum emission is decomposed into extended dust thermal emission ( spectral index \sim - 2.4 ) and compact emission from radio photosphere ( spectral index \sim - 2.0 ) .