低能质子同步加速器在材料、空间技术、核医学、生物以及能源等方面有着广泛的应用。本文将完成一个质子同步加速器的物理设计，该装置主要应用领域将在辐射加固以及放疗。该加速器计划将至少6.25×10^10 个粒子从7MeV 加速到最高250MeV，然后将束流在在1 秒内被引出。加速器的基本磁聚焦结构采用了DBA 结构，为注入和引出留出了两个无色散的长直线段。为了结构简洁，横向聚焦主要通过四块二极磁铁14°的边缘角来实现。由于边缘角对twiss 参数影响较大，我们讨论了边缘角可接受的误差范围，并留出了一组四极磁铁用于调整环的工作点。考虑到一次要加速粒子数目，这里采用了H-离子剥离注入的方式注入。这里我们完成了注入段的物理设计，并估计了剥离膜引起束团的发射度增长。考虑到注入等候粒子俘获效率的问题，我们在注入传输段中加入了散束器将注入束流能散由2.24% 降低到0.78%。在现有注入的条件下，绝热俘获效率主要受制于高频腔电压。在综合考虑俘获效率与束团能散的条件下我们选择了高频腔最大有效电压。最后我们给出了1/3 共振引出的物理设计，根据现有条件确定了引出元件的布置，并使得hardt条件被满足。

Low energy proton syschrotron is widely used in the field such as materials, space technology, radionuclide medicine, biotechnology and energy. The physical design of the proton synchrotron was completed in this article, and our machine will be mainly used in radiation-hardened and radiotherapy.At least 6.25×10^10 protons will be accelerated from 7MeV to 250MeV，and then extracted uniformly in 1s. DBA structure was adopted, and two non-disperse drift space for injection and extraction was got. The lattice is quit brief, the beam is focused by 14° edge angle of the four main dipole. Because of the error of the face angle will change twiss parameters, the acceptable error range was discussed. Two quadrupole was added to adjust tunes. Taking into account the number of particles, $H^-$ ion charge extraction injection was selected. The physics design of injection transport line was finished and then we estimated the emittance growth caused by stripping foil. To improve the adiabatic capture efficiency, a debuncher was used to reduce the energy spread from 2.24% to 0.78%. After injection, adiabatic capture efficiency is mainly limited by the voltage of the RF cavity. The maximum effective voltage of RF cavity is choosed after considering both capture efficiency and energy spread.Finally, the physical design of 1/3 resonant extration was completed, and the extracion element was layed out， and the Hardt Condition was satisfied.