The etching characteristics of the tracks of high dose alpha particles and protonsin domestic CR-39 detector were studied. By testing the environmental backgroundof the target chamber during the irradiation

it is shown that the ions recorded atarea so far as 40mm from beam spot are same to those at beam spot and that it isdifficult to identify etched tracks due to heavy overlap of tracks induced by high doseirradiation. However the other experiment indicates that the recording ionscharacteristic at etched area of high dose not change. The variation of the averageetch pit diameter in CR-39 as a funtion of the energy of alpha particles and protonswas given.