The ionization process of the interaction of nonmonochromatic laser with isotope atom system is studied. The multimode laser field is described by a stochastic model of chaotic field. By using the Fokker-Planck equation, the excited dynamic equation ofinteraction of the finite-bandwidth chaotic fields with K-level atom is derived. The influences of laser bandwidth and intensity on ionization efficiency and selectivity of three-level isotope atoms are also discussed.