Abstract: The collecting electrode is an important part of the two-dimensional air-ionization chamber dose detector, which affects the accuracy of dose measurement. In order to study the influence of collecting electrode on dose measurement, the Monte Carlo program EGSnrc was used for simulation calculation. The simulation involved photons with different energy, different materials (C, Al, Cu) for collecting electrode and different thicknesses of the collecting electrode (5.70 μm). The quantitative analysis based on the simulation was given. The results show that carbon is the best choice for collecting electrode within the process condition. When the copper is the only choice, the thickness of the electrode should be as small as possible and the measurement results need to be corrected.