The refractive indices along arbitrary wave vector direction were analyzed in uniaxial crystal with buried optical axis. When the optical axis is in the plane of incidence,the reflectivity fitting functions of s- and p-polarized light are presented. Then, the changes of reflectivity with incident angle have been measured with a modified reflectivity scanner, in s- and p-polarized light for CaCO3 crystal respectively. Using a fitting of experimental data based on reflectivity fitting functions the two principal refractive indices were obtained, no=1.6559, and ne=1.4851. This technique does not need sample machining, and the accuracy reaches 0.0001. Otherwise,in the case of unknown optical axis, the optical axis direction was determined with the Brewster angles of the three crystal surfaces measured by using the improved Brewster angle technique.