Abstract: The 2D ion-chamber array detector is widely used for dose measurement in radiotherapy due to its accuracy, instantaneity and repeatability. The 2D ion-chamber array detector is made of an array of small parallel-plate ion-chambers, which mainly comprise air cavity with wall surrounded. According to cavity theory on dose measurement, most ionization electrons in cavity come from the interaction of secondary electrons produced from chamber wall and air in cavity. Thus studying the effect of chamber wall in 2D ion-chamber array detector plays an important role in optimization design of 2D ion-chamber array detector. The Monte Carlo simulation method was used to analyze the relationship between the wall thickness and the amount of secondary electrons produced in different parts of chamber wall irradiated by incident photons of different energy and the influence of array structure on chamber-chamber crosstalk. It is shown that most secondary electrons are produced in the front wall whose thickness should be greater with photon energy increasing. It is also shown that the surface zone with thickness of only 2.3 mm in the side and back walls make a contribution to the amount of secondary electrons entering into air cavity, which is not sensitive to the incident photon energy. And the chamber-chamber crosstalk is directly related to the side wall thickness and the photon energy rather than the air cavity size. The results are of significance to the development of new design criterions on 2D ion-chamber array detector.