In the fusion plasmas, impurity behavior is important issue because of radiation loss and plasma-wall interactions. Spectroscopic measurements were carried out in the GAMMA 10 tandem mirror in order to investigate impurity transfer and plasma diagnostics. Oxygen ions were strongly emitted in the central cell of GAMMA 10. Then we have developed the collisional-radiative model for lower charge state of oxygen ions. The spatial profiles of OII, OIII, OIV and OV spectra were observed by the absolutely calibrated ultraviolet/visible spectrometer. Further more, spatial density profiles of O+, O2+, O3+ and O4+ were evaluated by the comparison of measurements and the CR-model calculation.