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A proton therapy facility based on a linac injector and a slow-cycling synchrotron is proposed.To obtain good treatments for different cancer types,both the spot scanning method and the double-scattering method are adopted in the facility,whereas the nozzles include both gantry and fixed beam types.The proton accelerator chain includes a synchrotron of 250 MeV in maximum energy,an injector of 7 MeV consisting of an RFQ and a DTL linac,with a repetition rate of 0.5 Hz.The slow extraction using the third-order resonance and together with the RFKO method is considered to be a good method to obtain a stable and more-or-less homogenous beam spill.To benefit the spot scanning method,the extraction energy can be as many as about 200 between 60 MeV and 230 MeV.A new method - the emittance balancing technique of using a solenoid or a quadrupole rotator is proposed to solve the problem of unequal emittance in the two transverse planes with a beam slowly extracted from a synchrotron.The facility has been designed to keep the potential to be upgraded to include the carbon therapy in the future.