The multi-strip ionization chamber functions as a location and dosage monitor for the Compact LAser Plasma Accelerator II (CLAPA II) beam delivery system, allowing laser pulse beam diagnostics. The properties of the planned ionization chamber were studied using Boag’s theory and Monte Carlo simulation in this research, and the energy loss and gain of 40 MeV–230 MeV proton beams in the parallel plate ionization chamber were simulated by SRIM tools and FLUKA program. The effects of various working gases on proton beam energy loss are explored, and some reference opinions are supplied for later working gas selection. The collecting efficiency of the ionization chamber under various deviations was determined using Boag’s theory. The findings reveal that when the ionization chamber air gap is 7mm and the bias voltage is over 1000V, the ionization chamber’s secondary particle collection efficiency may reach more than 90%. When the proton beam intensity is 1pA, and the gain of the ionization chamber is calculated, the detector’s output current may reach the order of 6 nA.