A spectral study of the Be/X-ray binary LSI+61° 303

New optical intermediate dispersion spectra of the periodic radio star LSI +61 degrees 303 are presented. The H-alpha emission line shows a typical shell absorption spectrum, which means that the primary of this Be/X ray binary may be a nearly equator-on Be star. The H-alpha emission line profile and its variation are analyzed, and some parameters such as the H-alpha EW and V/R peak ratio change strongly near the radio maximum, and may exhibit periodic variability. instead of having a wider minimum lasting for about half an orbital cycle as radio flux and V magnitude do, the H-alpha EW shows a deep minimum at phase similar to 0.75. The accretion disk around the neutron star formed near its periastron passage is suggested to be responsible for the change when it eclipses the primary and its envelope.