Shock ignition is considered as a relatively robust way to achieve the efficient fuel burn in inertial confinement fusion. However it requires intense laser pulses of sub-ns to launch strong convergent shock to ignite the pre-compressed target. Here we present a novel method, which has a substantially high extraction efficiency, to amplify laser pulses of ～200 ps for shock ignition. In this method, stacking pulse with a Stokes light of ～200 ps in the front and a pump light of ～5 ns following, is employed to propagate in the amplifier to extract the stored energy, then in the final system after harmonic conversion, laser energy is transferred from pump pulse to probe pulse by stimulated Brillouin scattering. Because of employing long pulse in the main amplifier, an output laser energy of 1520 kJ is achievable at fundamental frequency. Simulations show that the energy transfer efficiency is up to 75%, considering harmonic conversion efficiency of 60%80%, implying that 510 kJ laser pulses of ～200 ps can be produced using this scheme. As a result, only ～20 beams are required to generate the ignitor, reducing the cost for realizing the shock ignition.