Characteristics of helicon plasma in a 45 cm long discharge tube were diagnosed by the Langmuir electrostatic probe, optical emission spectroscopy (OES), and integrated capacitively coupled detector (ICCD). The discharge in helical wave mode was confirmed by the sharply variation of electron density and electron temperature based on the Langmuir data. We have noticed that the variation of electron density measured by the Langmuir electrostatic-probe is consistent with the OES measurement. Intensities in the spectra of argon atoms and ions are strongly related to discharge modes. The photos taken by ICCD can distinguish the discharge modes in the radial region. Intensity changes in the radial region reflect the electron motivation and the energy transfer path in the helicon plasma.