The electron trapping at high-field and detrapping in thin thermally nitrided silicon oxide (SiOxNy) films are studied in the present work. It is observed that when the nitridation degree is the lighter, with the increasing of the nirridation time the effective electron trap surface concentration in the films increases rapidly, and the detrapping ratio of trapped electrons is almost zero and independent of the shorting time for samples and the strength (until 8MV/cm) and duration of application of external reverse field, and the depth of the electron trap level is the deeper; when the nitridation degree is the heavier with the further increasing of the nitridation time the effective electron trap surface concentration decreases and the depth of electron trap level becomes shallow gradually, and the detrapping ratio of trapped electrons gradually increases and is approximately dependent exponentially on the strength and duration of time application of external reverse field and is almost independent of the shorting time for the samples.