Abstract: A high intensity proton cyclotron is under construction at China Institute of Atomic Energy for boron neutron capture therapy (BNCT), whose current is larger than 1 mA and extracted beam energy is 14 MeV. Compared with 400 μA beam current PET cyclotron, larger phase acceptance and better axial focusing are required for BNCT high intensity proton cyclotron. To accelerate and extract the milliampere-scale current, a series of optimizations were adopted, such as increasing the energy injected by negative hydrogen beam, increasing the aperture of shimming bars, using stepped structure to increase the head angle of Dee tip, and adjusting the height of entrance and exit of acce-leration clearance, which lead larger phase acceptance and better axial electric focusing. Axial focusing with different heights of Dee gaps was acquired by numerical calculation to adopt the optimal heights. The space charge effect was concluded in calculation and beam sizes at different currents were simulated. The simulation at measured magnetic field shows that the beam centering is better than 0.5 mm, the phase acceptance is larger than 40° and the 3 mA beam can be accelerated. The new central region is being machined at present.