According to VSEPR theory, the stable electronic structure of  ClF3 molecule is

lone pairs cause more repulsions as compared to bond pairs. If both the lone pairs occupy equatorial positions they experience minimum repulsions (each lp has only two 90° repulsions with bp);. If lone pairs occupy axial positions they experience maximum repulsions (each lp has three 90° repulsions with bp);Thus both the lone pairs occupy equatorial positions;