  To ensure the validity of quantum error-correction, the channel fidelity of
the noise channel is asked to be above the error-correction threshold. In most
cases, the channel fidelity of the quantum channel is below the
error-correction threshold, and it is necessary to study how to deal with these
channels. It is found that quantum error-correction can be used to classify the
independent quantum channel into 5 types, and 4 of the 5 types can be purified
with quantum error-correction. This work extends the applied range of quantum
error-correction, for example, providing a method to trace the source of the
quantum channel according to the effective channel and making some flexible
applications for quantum computation.
