In direct-drive laser fusion, the laser-target coupling efficiency can be enhanced and therefore the necessary driving laser energy can be reduced if the laser spot is zoomed with the target during implosion. A focal zooming is realized by image relay, in which the laser pulse is separated and split by the prism in an optical swithch. By this scheme, the laser energy would not be wasted and that some multiple splitting ways and pulse shaping become possible. A three- stage focus zooming system of XeCl laser is established and the zooming process is recorded by a streak camera. The experimental results suggest that the edge gradient between the stages is determined by that of the driving pulse for the Pockels cell in the switch.