Because of the extremely high saturation gain of a diode-pumped alkali laser(DPAL), the master oscillator power-amplifier(MOPA) system is an ideal selection to achieve power-scaling of DPALs. In this report, a theoretical model based on the kinetic algorithm was established for construction of the 3-stage amplification configuration in which the end-pumped structures were adopted. Then the amplification factors at different temperatures were calculated when the cell lengths in the MOPA system are 3, 5, and 7 cm, respectively. According to the simulation results, a 3 cm-long vapor cell was employed for the pre-amplification, a 5 cm-long vapor cell was chosen for the first main-amplification, and a 7 cm-long cell was used for the second main-amplification. With such a designed MOPA system, the output power over 1 000 W for a 50 mW Rb-DPAL seed light can be optained. In addition, the power of fluorescence and generated heat are evaluated for this 3-stage MOPA system. The research could provide some design schemes and theoretical methodology for realization of a power-scaled DPAL-MOPA system.