According to VSEPR theory, the stable electronic structure of  ${\mathrm{ClF}}_3$ 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;