The characteristics of polyethyleneterephthalate （PETP） solid state nuclear track detector on registering fission fragment tracks are studied. The variations of average diameter of fission fragment tracks with etching temperature

etching time and etchant concentration were measured. It is shown that among the three factors the influence of etching temperature on fission fragment tracks is the greatest. The PETP detectors were irradiated with low energy 16O heavy ions and the calibration curve was obtained.