Abstract: Proton accelerator is an appropriate device for providing neutron source for accelerator-based boron neutron capture therapy (AB-BNCT). The intensity and the spectrum of proton accelerator driven neutron source are more adjustable than reactor neutron source. The physical analysis of neutron target is the premise for an accelerator neutron source design, and it gives requirements of the accelerator parameters, like proton energy and beam current. Besides, it also provides parameters for structural design of neutron target and assembles for shaping and shielding. In this paper, Monte Carlo program MCNPX was used. After analyzing neuron yield, neutron spectrum, energy deposition, radioactivity of the target and neutron emitting angle distribution, an optimized design proposal for the ABBNCT neutron source was presented as 2.5 MeV proton beam bombarding with lithium target of 100 μm to 200 μm thickness. The neutron source is designed with an intensity of 9.74×10¹¹ s^-1 from per 1 mA incident proton. And the current of the proton beam is suggested as 15 mA, which will accumulate a radioactivity of the target material within 1.44×10¹³ Bq.