The construction of the new laser-driven proton therapy facility (CLAPA-II), designed by Peking University, has begun in Beijing. This paper describes the design of a cavity beam position monitor (CBPM) for the CLAPA-II. The proton beam which is accelerated to 100 MeV by 2-PW Laser has parameters of 108∼1010 particles range, 1 Hz repetition rate, 20∼40 mm beam length range. A non-interceptor BPM is needed to characterize the beam motion state in real time. The simulation has been performed to study CBPM properties and cross-talk.