We have investigated numerically the thermal recovery of the large aperture multi0segment amplifiers in the paper. With AMPHR3D, which is a thre-dimensional transient finite element heat transfer code, the temperature of Na:glass slab is investigated in detial, Preliminary thermal analysis indicates that active cooling with 4.7 10- 3m3s- 1 per flash lamp in lamp cassette cooperated with 7.6 10- 3m3s- 1 per slab cavity is sufficient to meet the 4 hour shot period of the lser system.