Co2-xMn1+xSi films with various composition x were epitaxially grown using molecular beam epitaxy (MBE). High crystallinity and atomic ordering in the prepared Co2-xMn1+xSi films were observed, and their magnetic damping and anisotropic magnetoresistance (AMR) effect were systematically investigated. An ultra-low magnetic damping constant of 0.0007 was obtained in the Co2-xMn1+xSi film with a valence electron number (NV) of about 29.0. Additionally, a relatively large negative AMR effect was observed in the Co2-xMn1+xSi films that had a NV of about 29.0. This low damping and the large negative AMR effect indicate that epitaxial Co2-xMn1+xSi films with high atomic ordering grown by MBE possess a high-spin polarization.