Absolute photoabsorption spectrum of CO molecule in the region 14—20 eV(620—890 Å) is measured using synchrotron radiation and multi-stage photoionization chamber, and its ionization energy is obtained. According to the absorption spectrum of CO and theoretical calculation, the Rydberg series converging to the Χ2Σ+, Α2Π, and B2Σ+ states of CO+ are assigned separately. Rydberg series assigned before are extended, Rydberg series converging to the Χ2Σ+ (ν+=2 and 3) of CO+, and n=2 (the real value of n is 3) progressions of the series converging to the Α2Π state of CO+ are identified. At the same time, the absorption spectrum of CO in the region 17.0—17.5 eV (710—730 Å) is also discussed deeply.