We investigate a theoretical model to accurately predict the output performances of slab laser amplifiers, which is one of the key issues in the study of space-based lasers. The realistic absorbed pump energy density, which induces nonuniformity of stored energy density in the laser medium, is introduced into the model. Using this model, the amplification performances of two space-based laser amplifiers with different pump configurations are compared. The results indicate that the bounce-pumped amplifier (BPA) achieves much higher output energy and efficiency compared with the side-pumped amplifier (SPA); it is also more suitable for space-based lasers.1. F. E. Hovis, J. Edelman, T. Schum, J. Rudd, and K. Andes, Proc. SPIE 6871, 68710E (2008).2. J. Luttmanna, K. Nicklausa, V. Morascha, S. Fua, M. Hofera, M. Trauba, H. D. Hoffmanna, R. Treichelb, C. Wuhrerc, and P. Zellerc, Proc. SPIE 6871, 687109 (2008).3. A. W. Yu, S. X. Li, G. B. Shaw, A. Seas, M. A. Stephen, E. Troupaki, A. Vasilyev, L. Ramos-Izquierdo, A. Lukemier, W. Mamakos, A. Melak, J. Guzek, and A. Rosanova, Proc. SPIE 7193, 719305 (2009).4. F. E. Hovis, N. Martin, and R. Burnham, Proc. SPIE 5798, 101 (2005).5. L. M. Frantz and J. S. Nodvik, J. Appl. Phys. 34, 2346 (1963).6. T. J. Kane, J. M. Eggleston, and R. L. Byer, IEEE J. Quantum Electron. 1, 1195 (1985).7. A. K. Sridharan, S. Saraf, and R. L. Byer, Appl. Opt. 46, 7552 (2007).8. J. M. Eggleston, L. M. Frantz, and H. Injeyan, IEEE J. Quantum Electron. 25, 1855 (1989).9. T. Rutherford, W. M. Tulloch, E. K. Gustafson, and R. L. Byer, IEEE J. Quantum Electron. 36, 205 (2000).