This paper discusses the influences of the refractive index change resulting from gas heating in the transverse-flow electrical discharge COa laser on the optical axis and the transverse mode. The calculation indicates that tho first order quantity of the refractive index change will vary the position and tho angle of the laser axis. Tho second order quantity of tho refractive index change is analogous to the negative lens effect in the axisymmetrical discharge tube1. Both effects will be enhanced with the increase of injection power and the mixture pressure, especially with the gain length.