Eigenquantum defects μα and transformation matrix Uiα of La+ are calculated from the first principles by relativistic multichannel theory, and dipole matrix elements Dα axe obtained by fitting the experimental spectra.With these parameters, ionic autoionization spectra of lanthanum via an intermediate state (Xe)5d6d 1P1 of La+in the energy region of 90650-91500 cm -1 are calculated within the framework of multichannel quantum defect theory. Our calculated spectra are in general agreement with the experimental data.